Update build scripts to avoid deprecation warnings with Gradle 8

Closes gh-38

build.gradle

@@ -18,7 +18,7 @@ ext {
 }
 
 
-version project.projectVersion
+version = project.projectVersion
 
 apply plugin:'idea'
 
@@ -42,12 +42,12 @@ nexusPublishing {
 
 subprojects { project->
     if (project.name.startsWith('grace-plugin')) {
-        group "org.graceframework.plugins"
+        group = "org.graceframework.plugins"
     }
     else {
-        group "org.graceframework"
+        group = "org.graceframework"
     }
-    version project.projectVersion
+    version = project.projectVersion
 
     if (project.name.startsWith('examples') || project.name.endsWith('docs')) {
         return

grace-async-rxjava/build.gradle

@@ -2,6 +2,3 @@ dependencies {
     api project(":grace-async-core")
     implementation "io.reactivex:rxjava:$rxJavaVersion"
 }
-
-
-

publishing/mavenCentral.gradle

@@ -29,10 +29,10 @@ publishing {
         maven(MavenPublication) {
             def projectName = project.name.split('-')*.capitalize().join(' ')
             if (project.name.startsWith('grace-plugin')) {
-                artifactId(project.name - 'grace-plugin-')
+                artifactId = project.name - 'grace-plugin-'
             }
             else {
-                artifactId project.name
+                artifactId = project.name
             }
             from components.java
 
@@ -85,7 +85,7 @@ jar {
 
 afterEvaluate {
     signing {
-        required { isReleaseVersion && gradle.taskGraph.hasTask("publish")  }
+        required = isReleaseVersion && gradle.taskGraph.hasTask("publish")
         sign publishing.publications.maven
     }