enable GitHub Actions CI (#1709)

.github/workflows/ci.yml

@@ -0,0 +1,32 @@
+name: CI
+
+on:
+  pull_request:
+    branches:
+      - master
+  push:
+    branches:
+      - master
+
+jobs:
+  build:
+    runs-on: ubuntu-20.04
+    strategy:
+      matrix:
+        java: [ '8', '11', '15' ]
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up JDK
+      uses: actions/setup-java@v1
+      with:
+        java-version: ${{ matrix.java }}
+    - name: print Java version
+      run: java -version
+    - uses: actions/cache@v2
+      with:
+        path: ~/.m2/repository
+        key: ${{ runner.os }}-maven-${{ hashFiles('**/pom.xml') }}
+        restore-keys: |
+          ${{ runner.os }}-maven-
+    - name: Build
+      run: mvn --no-transfer-progress -B clean package --file pom.xml