Test if jdk 7 works (as jdk 6 is not available in Mac

.github/workflows/main.yml

@@ -29,10 +29,10 @@ jobs:
   macos-build:
     runs-on: macos-latest
     steps:
-      # java 6 is required for using closure compiler
+      # java 7 is required for using closure compiler
       - uses: actions/setup-java@v1
         with:
-          java-version: '9.0.4' # The JDK version to make available on the path.
+          java-version: '7' # The JDK version to make available on the path.
           java-package: jdk # (jre, jdk, or jdk+fx) - defaults to jdk
           architecture: x64 # (x64 or x86) - defaults to
       - uses: actions/checkout@v2