Add ESLint to GitHub Actions

.github/workflows/lint.yml

@@ -0,0 +1,15 @@
+name: ESLint
+on: push
+jobs:
+  lint:
+    runs-on: ubuntu-20.04
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-node@v1
+        with:
+          node-version: '12'
+
+      - name: Check ESLint
+        run: |
+          yarn install
+          yarn run lint