Switch to GitHub Actions for CI linting (#10)

Author: jparise

.github/workflows/ci.yml

@@ -0,0 +1,25 @@
+name: CI
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v1
+    - uses: actions/setup-node@v1
+      with:
+        node-version: '10.x'
+    - name: Install dependencies
+      run: |
+        npm install -g markdownlint-cli
+    - name: Lint markdown files
+      run: |
+        markdownlint *.md