Migrate to GitHub Actions (#18)

* Delete .travis.yml
diff --git a/.github/workflows/test-package.yml b/.github/workflows/test-package.yml
new file mode 100644
index 0000000..21a3c50
--- /dev/null
+++ b/.github/workflows/test-package.yml
@@ -0,0 +1,61 @@
+name: Dart CI
+
+on:
+  # Run on PRs and pushes to the default branch.
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+  schedule:
+    - cron: "0 0 * * 0"
+
+env:
+  PUB_ENVIRONMENT: bot.github
+
+jobs:
+  # Check code formatting and static analysis on a single OS (linux)
+  # against Dart dev.
+  analyze:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        sdk: [dev]
+    steps:
+      - uses: actions/checkout@v2
+      - uses: dart-lang/setup-dart@v0.3
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Check formatting
+        run: dart format --output=none --set-exit-if-changed .
+        if: always() && steps.install.outcome == 'success'
+      - name: Analyze code
+        run: dart analyze --fatal-infos
+        if: always() && steps.install.outcome == 'success'
+
+  # Run tests on a matrix consisting of two dimensions:
+  # 1. OS: ubuntu-latest, (macos-latest, windows-latest)
+  # 2. release channel: dev
+  test:
+    needs: analyze
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        # Add macos-latest and/or windows-latest if relevant for this package.
+        os: [ubuntu-latest]
+        sdk: [dev]
+    steps:
+      - uses: actions/checkout@v2
+      - uses: dart-lang/setup-dart@v0.3
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Run VM tests
+        run: dart test --platform vm
+        if: always() && steps.install.outcome == 'success'
diff --git a/.travis.yml b/.travis.yml
deleted file mode 100644
index adcaa68..0000000
--- a/.travis.yml
+++ /dev/null
@@ -1,18 +0,0 @@
-language: dart
-
-dart:
-  - dev
-
-dart_task:
-  - dartfmt
-  - dartanalyzer: --fatal-warnings --fatal-infos .
-  - test
-
-# Only building master means that we don't run two builds for each pull request.
-branches:
-  only: [master]
-
-# Incremental pub cache and builds.
-cache:
-  directories:
-  - $HOME/.pub-cache