Replaces Travis CI with GitHub Actions (#625)

.github/workflows/main.yml

@@ -0,0 +1,60 @@
+name: Flutter CI
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+  workflow_dispatch:
+  schedule:
+    - cron: '0 0 * * *' # Every day at midnight
+
+jobs:
+  flutter-tests:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - flutter_version: dev
+            allow_failure: true
+          - flutter_version: beta
+            allow_failure: true
+          - flutter_version: stable
+            allow_failure: false
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-java@v1
+        with:
+          java-version: '12.x'
+      - uses: subosito/flutter-action@v1
+        with:
+          channel: ${{ matrix.flutter_version }}
+      - run: ./tool/flutter_ci_script.sh
+        continue-on-error: ${{ matrix.allow_failure }}
+  android-build:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-java@v1
+        with:
+          java-version: '12.x'
+      - uses: subosito/flutter-action@v1
+        with:
+          channel: stable
+      - run: ./tool/android_ci_script.sh
+  ios-build:
+    runs-on: macos-latest
+    strategy:
+      fail-fast: false
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-java@v1
+        with:
+          java-version: '12.x'
+      - uses: subosito/flutter-action@v1
+        with:
+          channel: stable
+      - run: ./tool/ios_ci_script.sh