Test on JDK 15.

Author: michael-simons

.github/workflows/build.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        java: [ '8', '11', '14' ]
+        java: [ '8', '11', '15' ]
     steps:
       - uses: actions/checkout@v1
       - name: Set up JDK