lintをGitHub Actions でするように (#6101)

* package.json の lint スクリプトを修正

* lint アクションを追加

* yarn lint --fix

* 手動修正

.github/workflows/nodejs.yml

@@ -41,3 +41,13 @@ jobs:
       run: yarn build
     - name: Test
       run: yarn test
+
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - uses: actions/setup-node@v1
+      with:
+        node-version: 12.x
+    - run: yarn install
+    - run: yarn lint