fix docs build (#75)

Author: Archmonger

.github/workflows/publish-docs.yml

@@ -11,5 +11,5 @@ jobs:
       - uses: actions/setup-python@v2
         with:
           python-version: 3.x
-      - run: pip install requirements/build-docs.txt
+      - run: pip install -r requirements/build-docs.txt
       - run: mkdocs gh-deploy --force