Add GitHub Action for running CI tests.

.github/workflows/nodejs.yml

@@ -0,0 +1,24 @@
+name: Node.js CI
+
+on: [push, pull_request]
+
+jobs:
+  build:
+
+    runs-on: ${{ matrix.os }}
+
+    strategy:
+      matrix:
+        os: [macos-latest, ubuntu-latest, windows-latest]
+        node-version: [8.x, 10.x, 12.x]
+
+    steps:
+    - uses: actions/checkout@v1
+    - name: Use Node.js ${{ matrix.node-version }}
+      uses: actions/setup-node@v1
+      with:
+        node-version: ${{ matrix.node-version }}
+    - name: Install Dependencies
+      run: npm install --no-package-lock
+    - name: Run Tests
+      run: npm run ci