Run npm install.

Author: Anduin2017

.github/workflows/ci.yml

@@ -19,6 +19,7 @@ jobs:
         run: mdl . -r ~MD036,~MD024,~MD004,~MD029
       - run: pip install -r requirements.txt
       - run: mkdocs build --strict
+      - run: npm install
       - run: node .github/manual_lint.js
         # Suppress 036 Emphasis used instead of a header
         # Suppress 024 Multiple headers with the same content