Test Java 11

Author: Nikos Papailiou

.github/workflows/github_actions.yml

@@ -21,7 +21,7 @@ jobs:
         uses: actions/setup-java@v2
         with:
           distribution: 'adopt'
-          java-version: '8'
+          java-version: '11'
           check-latest: true
 
       - run: |