migrate fpb-lint from travisci to gh actions (#5186)

.github/workflows/fpb-lint.yml

@@ -0,0 +1,17 @@
+name: free-programming-books-lint
+
+on: [push]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Use Node.js
+      uses: actions/setup-node@v1
+      with:
+        node-version: '6.x'
+    - run: npm install -g free-programming-books-lint
+    - run: fpb-lint .