Added github action to build on each push

First try without workaround for openjdk7

.github/workflows/ci.yaml

@@ -0,0 +1,26 @@
+---
+name: Java CI
+
+on: [push]
+
+jobs:
+  test:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-18.04]
+        java: [7, 8, 9, 11, 14, 15]
+      fail-fast: false
+      max-parallel: 4
+    name: Test JDK ${{ matrix.java }}, ${{ matrix.os }}
+
+    steps:
+      - uses: actions/checkout@v1
+      - name: Set up JDK
+        uses: actions/setup-java@v1
+        with:
+          java-version: ${{ matrix.java }}
+      - name: Build with Gradle
+        run: ./gradlew clean build javadoc
+
+...