ci: run ESLint, too

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

.github/workflows/test.yml

@@ -15,6 +15,7 @@ jobs:
       - uses: actions/checkout@v2
       - run: npm ci
       - run: npm run build
+      - run: npm run lint
       - run: npm run test
       - run: npm run package
       - name: Verify that `dist/index.js` is up to date