Chore: Use GitHub Actions (#123)

* Chore: Use GitHub Actions

* Lint source only once in CI

This runs the tests against all supported major versions of Node.js, but
we only need to lint the source code once.

Author: btmills

.github/workflows/ci.yml

@@ -0,0 +1,43 @@
+name: CI
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+jobs:
+  lint:
+    name: Lint
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v1
+    - name: Install Node.js
+      uses: actions/setup-node@v1
+    - name: Install Packages
+      run: npm install
+      env:
+        CI: true
+    - name: Lint
+      run: npm run lint
+
+  test:
+    name: Test
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        node-version: [6.x, 8.x, 9.x, 10.x, 12.x]
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v1
+    - name: Install Node.js ${{ matrix.node-version }}
+      uses: actions/setup-node@v1
+      with:
+        node-version: ${{ matrix.node-version }}
+    - name: Install Packages
+      run: npm install
+      env:
+        CI: true
+    - name: Test
+      run: npm run test-cov