GitHub Actions: initial commit

.github/workflows/ci.yml

@@ -0,0 +1,23 @@
+# https://help.github.com/actions/language-and-framework-guides/building-and-testing-java-with-gradle
+
+name: CI
+
+on:
+  push:
+    branches: [github-actions]
+  pull_request:
+    branches: [github-actions]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up JDK 1.8
+      uses: actions/setup-java@v1
+      with:
+        java-version: 1.8
+    - name: Build with Gradle
+      run: ./gradlew build