Create ci.yml

Add GitHub CI Action for testing purposes.

Signed-off-by: Jerome Luckenbach <github@luckenba.ch>

.github/workflows/ci.yml

@@ -0,0 +1,32 @@
+name: CI
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  build:
+    # Run the CI build for all relevant systems
+    strategy:
+      matrix:
+        os: [macos-latest, ubuntu-latest, windows-latest]
+    runs-on: ${{ matrix.os }}
+    steps:
+    
+    - name: Checkout
+      uses: actions/checkout@v2
+      
+    - name: Install Node.js
+      uses: actions/setup-node@v1
+      with:
+        node-version: 10.x
+        
+    - run: npm install
+    
+    - run: xvfb-run -a npm test
+      if: runner.os == 'Linux'
+      
+    - run: npm test
+      if: runner.os != 'Linux'