Add CI job that lints VimL and reviews PRs

.github/workflows/vint.yml

@@ -0,0 +1,15 @@
+name: Vint
+on: [push, pull_request]
+jobs:
+  vint:
+    strategy:
+      fail-fast: false
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout
+      uses: actions/checkout@master
+    - name: Run vint with reviewdog
+      uses: reviewdog/action-vint@v1.0.1
+      with:
+        github_token: ${{ secrets.github_token }}
+        reporter: github-pr-review