Make sure travis doesn't fail for PRs due to coveralls

.travis.yml

@@ -42,15 +42,15 @@ jobs:
   include:
   # We grab the appropriate GHC and cabal-install versions from hvr's PPA. See:
   # https://github.com/hvr/multi-ghc-travis
-  - env: BUILD=stack ARGS="--resolver lts-11.22 --stack-yaml stack-old.yaml"
+  - env: BUILD=stack ARGS="--resolver lts-11.22" STACK_YAML="--stack-yaml stack-old.yaml"
     compiler: ": #stack 8.2.2"
     addons: {apt: {packages: [libgmp-dev]}}
 
-  - env: BUILD=stack ARGS="--resolver lts-12.26 --stack-yaml stack-old.yaml"
+  - env: BUILD=stack ARGS="--resolver lts-12.26" STACK_YAML="--stack-yaml stack-old.yaml"
     compiler: ": #stack 8.4.4"
     addons: {apt: {packages: [libgmp-dev]}}
 
-  - env: BUILD=stack ARGS="--resolver lts-14.27" COVERALLS_STACK_YAML="stack-coveralls.yaml"
+  - env: BUILD=stack ARGS="--resolver lts-14.27" STACK_YAML="--stack-yaml stack-old.yaml" COVERALLS_STACK_YAML="stack-coveralls.yaml"
     compiler: ": #stack 8.6.5"
     addons: {apt: {packages: [libgmp-dev]}}
 
@@ -137,7 +137,7 @@ script:
          travis_retry curl -L https://github.com/lehins/stack-hpc-coveralls/releases/download/0.0.5.0/shc.tar.gz | tar xz shc
          STACK_YAML="$COVERALLS_STACK_YAML" ./shc --repo-token=$COVERALLS_REPO_TOKEN combined custom
       else
-         stack --no-terminal $ARGS test $BUILD_ARGS
+         stack --no-terminal $ARGS $STACK_YAML test $BUILD_ARGS
       fi
       ;;
     cabal)