ci: add Code Scanning workflow (#381)

.github/workflows/codeql.yml

@@ -0,0 +1,29 @@
+name: "Code Scanning"
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+
+jobs:
+  CodeQL-Build:
+    runs-on: ubuntu-18.04
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 2
+
+      - run: git checkout HEAD^2
+        if: ${{ github.event_name == 'pull_request' }}
+
+      - name: Initialize CodeQL
+        uses: github/codeql-action/init@v1
+        with:
+          languages: javascript
+
+      - name: Autobuild
+        uses: github/codeql-action/autobuild@v1
+
+      - name: Perform CodeQL Analysis
+        uses: github/codeql-action/analyze@v1