add android build workflow

.github/workflows/android.yml

@@ -0,0 +1,17 @@
+name: Android CI
+
+on: [push]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v1
+    - name: set up JDK 1.8
+      uses: actions/setup-java@v1
+      with:
+        java-version: 1.8
+    - name: Build with Gradle
+      run: ./gradlew build