Add a GitHub action for linting

.github/workflows/lint.yml

@@ -0,0 +1,10 @@
+name: Lint
+on: [push, pull_request]
+jobs:
+    lint:
+        runs-on: ubuntu-latest
+        steps:
+            - uses: actions/checkout@v2
+            - uses: Adzz/yarn_command_action@v1.0.0
+              with:
+                  command: lint