downgrade build to Java 11

Author: y-lakhdar

.github/workflows/build.yml

@@ -15,10 +15,10 @@ jobs:
 
     steps:
     - uses: actions/checkout@v2
-    - name: Set up JDK 16
+    - name: Set up JDK 11
       uses: actions/setup-java@v2
       with:
-        java-version: '16'
+        java-version: '11'
         distribution: 'adopt'
     - name: Build with Maven
       run: mvn -B package --file pom.xml