Create android.yml

This creates a GitHub Action for building and
testing the project, as an attempt to replace
Travis-CI.

.github/workflows/android.yml

@@ -0,0 +1,27 @@
+name: Android CI
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+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
+      run: ./gradlew assembleRelease
+    - name: Check lint
+      run: ./gradlew lintRelease
+    - name: Run unit tests
+      run: ./gradlew testReleaseUnitTest
+    - name: FindBugs
+      run: ./gradlew findbugs