Add workflow to run ESLint

.github/workflows/lint.yml

@@ -0,0 +1,17 @@
+name: Lint
+on:
+  push:
+    branches: [master]
+  pull_request:
+    types: [opened, synchronize]
+jobs:
+  lint:
+    name: Run ESLint
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v1
+    - uses: actions/setup-node@v1
+      with:
+        node-version: '12.x'
+    - run: npm install
+    - run: npm run lint