Gradle wrapper: upgrade to Gradle 4.8.1

With JDK 10, `./gradlew allTest` fails to run tests, instead spewing out
the following errors on the console:

    Exception in thread "main" java.lang.reflect.InvocationTargetException
            at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
            at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
            at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
            at java.base/java.lang.reflect.Method.invoke(Method.java:564)
            at java.instrument/sun.instrument.InstrumentationImpl.loadClassAndStartAgent(InstrumentationImpl.java:510)
    FATAL ERROR in native method: processing of -javaagent failed
            at java.instrument/sun.instrument.InstrumentationImpl.loadClassAndCallPremain(InstrumentationImpl.java:522)
    Caused by: java.lang.RuntimeException: Class java/lang/UnknownError could not be instrumented.
            at org.jacoco.agent.rt.internal_290345e.core.runtime.ModifiedSystemClassRuntime.createFor(ModifiedSystemClassRuntime.java:139)
            at org.jacoco.agent.rt.internal_290345e.core.runtime.ModifiedSystemClassRuntime.createFor(ModifiedSystemClassRuntime.java:100)
            at org.jacoco.agent.rt.internal_290345e.PreMain.createRuntime(PreMain.java:55)
            at org.jacoco.agent.rt.internal_290345e.PreMain.premain(PreMain.java:47)
            ... 6 more
    Caused by: java.lang.NoSuchFieldException: $jacocoAccess
            at java.base/java.lang.Class.getField(Class.java:1958)
            at org.jacoco.agent.rt.internal_290345e.core.runtime.ModifiedSystemClassRuntime.createFor(ModifiedSystemClassRuntime.java:137)
            ... 9 more

... and so forth

According to a PR[1] on the JaCoCo's issue tracker, this occurs because
"Classes of JDK 10 EA b35 use a new classfile version number and so
JaCoCo Agent 0.7.9 as well as agent from current build of master branch
fail to start". This has been fixed as of JaCoCo 0.8.1, which also
happens to be the latest release.

We do not explicitly specify the version JaCoCo to use in our
build.gradle file, and so the `jacoco` gradle plugin just uses its
default, which happens to be 0.8.0[2] on Gradle 4.6 (the version we are
using). This version of JaCoCo still has this bug, and so we get these
errors.

Fix this by upgrading to the latest version of Gradle (4.8.1). Since
Gradle 4.7[3] the default JaCoCo plugin has been upgraded to version
0.8.1, and so upgrading to the latest version of Gradle will fix this
problem and allow us to run tests on JDK 10.

The Gradle wrapper upgrade was performed by running the command:

    ./gradlew wrapper --gradle-version 4.8.1

and then converting the line endings of gradlew.bat to unix to satisfy
our travis line ending checks.

Also, update any references to the Gradle version we are using in the
code base to 4.8.1.

[1] jacoco/jacoco#629
[2] gradle/gradle@8a09484
[3] https://docs.gradle.org/4.7/release-notes.html#default-jacoco-version-upgraded-to-0.8.1

build.gradle

@@ -1,6 +1,6 @@
 // Gradle Configuration File
 // For more details take a look at the Java Quickstart chapter in the Gradle
-// user guide available at http://gradle.org/docs/4.6/userguide/tutorial_java_projects.html
+// user guide available at http://gradle.org/docs/4.8.1/userguide/tutorial_java_projects.html
 
 import org.gradle.api.tasks.testing.logging.TestLogEvent
 
@@ -75,7 +75,7 @@ shadowJar {
 }
 
 task wrapper(type: Wrapper) {
-    gradleVersion = '4.6'
+    gradleVersion = '4.8.1'
 }
 
 task coverage(type: JacocoReport) {

gradle/wrapper/gradle-wrapper.properties

@@ -1,6 +1,5 @@
-#Mon Mar 21 13:28:19 SGT 2016
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.8.1-bin.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-4.6-all.zip

gradlew

@@ -1,25 +1,43 @@
-#!/usr/bin/env bash
+#!/usr/bin/env sh
 
 ##############################################################################
 ##
 ##  Gradle start up script for UN*X
 ##
 ##############################################################################
 
-# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
-DEFAULT_JVM_OPTS=""
+# Attempt to set APP_HOME
+# Resolve links: $0 may be a link
+PRG="$0"
+# Need this for relative symlinks.
+while [ -h "$PRG" ] ; do
+    ls=`ls -ld "$PRG"`
+    link=`expr "$ls" : '.*-> \(.*\)$'`
+    if expr "$link" : '/.*' > /dev/null; then
+        PRG="$link"
+    else
+        PRG=`dirname "$PRG"`"/$link"
+    fi
+done
+SAVED="`pwd`"
+cd "`dirname \"$PRG\"`/" >/dev/null
+APP_HOME="`pwd -P`"
+cd "$SAVED" >/dev/null
 
 APP_NAME="Gradle"
 APP_BASE_NAME=`basename "$0"`
 
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS=""
+
 # Use the maximum available, or set MAX_FD != -1 to use that value.
 MAX_FD="maximum"
 
-warn ( ) {
+warn () {
     echo "$*"
 }
 
-die ( ) {
+die () {
     echo
     echo "$*"
     echo
@@ -30,6 +48,7 @@ die ( ) {
 cygwin=false
 msys=false
 darwin=false
+nonstop=false
 case "`uname`" in
   CYGWIN* )
     cygwin=true
@@ -40,31 +59,11 @@ case "`uname`" in
   MINGW* )
     msys=true
     ;;
+  NONSTOP* )
+    nonstop=true
+    ;;
 esac
 
-# For Cygwin, ensure paths are in UNIX format before anything is touched.
-if $cygwin ; then
-    [ -n "$JAVA_HOME" ] && JAVA_HOME=`cygpath --unix "$JAVA_HOME"`
-fi
-
-# Attempt to set APP_HOME
-# Resolve links: $0 may be a link
-PRG="$0"
-# Need this for relative symlinks.
-while [ -h "$PRG" ] ; do
-    ls=`ls -ld "$PRG"`
-    link=`expr "$ls" : '.*-> \(.*\)$'`
-    if expr "$link" : '/.*' > /dev/null; then
-        PRG="$link"
-    else
-        PRG=`dirname "$PRG"`"/$link"
-    fi
-done
-SAVED="`pwd`"
-cd "`dirname \"$PRG\"`/" >&-
-APP_HOME="`pwd -P`"
-cd "$SAVED" >&-
-
 CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
 
 # Determine the Java command to use to start the JVM.
@@ -90,7 +89,7 @@ location of your Java installation."
 fi
 
 # Increase the maximum file descriptors if we can.
-if [ "$cygwin" = "false" -a "$darwin" = "false" ] ; then
+if [ "$cygwin" = "false" -a "$darwin" = "false" -a "$nonstop" = "false" ] ; then
     MAX_FD_LIMIT=`ulimit -H -n`
     if [ $? -eq 0 ] ; then
         if [ "$MAX_FD" = "maximum" -o "$MAX_FD" = "max" ] ; then
@@ -114,6 +113,7 @@ fi
 if $cygwin ; then
     APP_HOME=`cygpath --path --mixed "$APP_HOME"`
     CLASSPATH=`cygpath --path --mixed "$CLASSPATH"`
+    JAVACMD=`cygpath --unix "$JAVACMD"`
 
     # We build the pattern for arguments to be converted via cygpath
     ROOTDIRSRAW=`find -L / -maxdepth 1 -mindepth 1 -type d 2>/dev/null`
@@ -154,11 +154,19 @@ if $cygwin ; then
     esac
 fi
 
-# Split up the JVM_OPTS And GRADLE_OPTS values into an array, following the shell quoting and substitution rules
-function splitJvmOpts() {
-    JVM_OPTS=("$@")
+# Escape application args
+save () {
+    for i do printf %s\\n "$i" | sed "s/'/'\\\\''/g;1s/^/'/;\$s/\$/' \\\\/" ; done
+    echo " "
 }
-eval splitJvmOpts $DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS
-JVM_OPTS[${#JVM_OPTS[*]}]="-Dorg.gradle.appname=$APP_BASE_NAME"
+APP_ARGS=$(save "$@")
+
+# Collect all arguments for the java command, following the shell quoting and substitution rules
+eval set -- $DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS "\"-Dorg.gradle.appname=$APP_BASE_NAME\"" -classpath "\"$CLASSPATH\"" org.gradle.wrapper.GradleWrapperMain "$APP_ARGS"
+
+# by default we should be in the correct project dir, but when run from Finder on Mac, the cwd is wrong
+if [ "$(uname)" = "Darwin" ] && [ "$HOME" = "$PWD" ]; then
+  cd "$(dirname "$0")"
+fi
 
-exec "$JAVACMD" "${JVM_OPTS[@]}" -classpath "$CLASSPATH" org.gradle.wrapper.GradleWrapperMain "$@"
+exec "$JAVACMD" "$@"

gradlew.bat

@@ -8,14 +8,14 @@
 @rem Set local scope for the variables with windows NT shell
 if "%OS%"=="Windows_NT" setlocal
 
-@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
-set DEFAULT_JVM_OPTS=
-
 set DIRNAME=%~dp0
 if "%DIRNAME%" == "" set DIRNAME=.
 set APP_BASE_NAME=%~n0
 set APP_HOME=%DIRNAME%
 
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS=
+
 @rem Find java.exe
 if defined JAVA_HOME goto findJavaFromJavaHome
 
@@ -46,10 +46,9 @@ echo location of your Java installation.
 goto fail
 
 :init
-@rem Get command-line arguments, handling Windowz variants
+@rem Get command-line arguments, handling Windows variants
 
 if not "%OS%" == "Windows_NT" goto win9xME_args
-if "%@eval[2+2]" == "4" goto 4NT_args
 
 :win9xME_args
 @rem Slurp the command line arguments.
@@ -60,11 +59,6 @@ set _SKIP=2
 if "x%~1" == "x" goto execute
 
 set CMD_LINE_ARGS=%*
-goto execute
-
-:4NT_args
-@rem Get arguments from the 4NT Shell from JP Software
-set CMD_LINE_ARGS=%$
 
 :execute
 @rem Setup the command line