Run SonarCloud analysis with Java 11

As pointed in issue #267, SonarCloud will drop support for Java 8 by
October 2020. This PR will run the SonarCloud analysis with Java 11,
while still using Java 8 source level.

Closes: #267
PR: #268

.github/workflows/actions.yml

@@ -38,7 +38,7 @@ jobs:
           restore-keys: ${{ runner.os }}-gradle-
       - name: Cache Sonar
         uses: actions/cache@v1
-        if: matrix.java == '8' && matrix.os == 'ubuntu'
+        if: matrix.java == '11' && matrix.os == 'ubuntu'
         with:
           path: ~/.sonar/cache/
           key: ${{ runner.os }}-sonar
@@ -47,7 +47,7 @@ jobs:
         with:
           arguments: --refresh-dependencies --stacktrace --scan clean build
       - name: Sonarqube
-        if: matrix.java == '8' && matrix.os == 'ubuntu'
+        if: matrix.java == '11' && matrix.os == 'ubuntu'
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           SONAR_TOKEN: "61ab2579215aa8a0024a2f9368fc1298fdecfd18"