Move CI to GitHub Actions (firebase#179)

Author: samtstern

.github/workflows/android.yml

@@ -0,0 +1,19 @@
+name: Android CI
+
+on:
+  - pull_request
+  - push
+
+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: Check Snippets
+      run: python scripts/checksnippets.py
+    - name: Build with Gradle
+      run: ./gradlew clean ktlint build

.travis.yml

@@ -8,4 +8,7 @@ on [firebase.google.com](https://firebase.google.com/docs/).
 We love contributions! See [CONTRIBUTING.md](./CONTRIBUTING.md) for guidelines.
 
 
-[![Build Status](https://travis-ci.org/firebase/snippets-android.svg?branch=master)](https://travis-ci.org/firebase/snippets-android)
+[![Actions Status][gh-actions-badge]][gh-actions]
+
+[gh-actions]: https://github.com/firebase/snippets-android/actions
+[gh-actions-badge]: https://github.com/firebase/snippets-android/workflows/Android%20CI/badge.svg