chore: add actions for different JDK versions (#90)

Author: Kristjan Kosic

.github/workflows/test.yml

@@ -11,13 +11,17 @@ on:
 jobs:
     unit:
         runs-on: ubuntu-latest
+        strategy:
+            matrix:
+                # test against latest update of each major Java version, as well as specific updates of LTS versions:
+                java: [ 8, 9, 10, 11, 12, 13 ]
 
         steps:
             - uses: actions/checkout@v1
-            - name: Set up JDK 1.8
+            - name: Use Java Version ${{ matrix.java }}
               uses: actions/setup-java@v1
               with:
-                  java-version: 1.8
+                  java-version: ${{ matrix.java }}
             - name: Install
               run: gradle dependencies
             - name: Test