Add Github Action

Author: filiphr

.github/workflows/main.yml

@@ -0,0 +1,19 @@
+name: Gem Main Build
+
+on: [push, pull_request]
+
+jobs:
+  test_jdk:
+    name: Linux (JDK ${{ matrix.java }})
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        java: [1.8, 11, 13, 14-ea]
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-java@v1
+        with:
+          java-version: ${{ matrix.java }}
+      - name: Verify
+        run: ./mvnw verify -B --no-transfer-progress -V