Re-introduce JDK matrix for CI pipeline

.github/workflows/continuous-integration-workflow.yml

@@ -11,16 +11,16 @@ jobs:
   build:
     name: Build
     runs-on: ubuntu-latest
-#    strategy:
-#      matrix:
-#        jdk: [8, 11]
-#      fail-fast: false
+    strategy:
+      matrix:
+        jdk: [8, 11]
+      fail-fast: false
     steps:
       - uses: actions/checkout@v2
-      - name: Set up JDK 8
+      - name: Set up JDK ${{ matrix.jdk }}
         uses: actions/setup-java@v1
         with:
-          java-version: '8'
+          java-version: ${{ matrix.jdk }}
       - name: Cache Gradle packages
         uses: actions/cache@v2
         with: