Run multiple java versions

Author: Oryan M

.github/workflows/pull-request.yml

@@ -5,13 +5,16 @@ on:
 jobs:
   build:
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        java: [ '8', '11', '15' ]
     steps:
       - name: Checkout
         uses: actions/checkout@v2
       - name: Setup java
         uses: actions/setup-java@v2
         with:
-          java-version: '11'
+          java-version: ${{ matrix.java }}
           distribution: 'adopt'
       - name: Cache Maven packages
         uses: actions/cache@v2