Use requirements.txt in github action

Author: fjp

.github/workflows/ci.yml

@@ -27,7 +27,5 @@ jobs:
       - uses: actions/setup-python@v2
         with:
           python-version: 3.x
-      - run: pip install mkdocs-material
-      - run: pip install mkdocs-jupyter
-      - run: pip install mkdocs-macros-plugin
+      - run: pip install -r requirements.txt
       - run: mkdocs gh-deploy --force