Adds CI workflow back in

.github/workflows/ci.yml

@@ -0,0 +1,22 @@
+name: Tests
+
+on: [push]
+
+jobs:
+  build:
+    strategy:
+      matrix:
+        os: [macos-latest, ubuntu-latest, windows-latest]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+      - name: Install Node.js
+        uses: actions/setup-node@v3
+        with:
+          node-version: 12.x
+      - run: npm install
+      - name: Run tests
+        uses: coactions/setup-xvfb@v1
+        with:
+          run: npm test