pip install upgrade for doc

.gitlab-ci.yml

@@ -77,7 +77,7 @@ pages:
     stage: deploy
     image: python:3.7-alpine
     script:
-      - pip install -r docs/doc_requirements.txt
+      - pip install -U -r docs/doc_requirements.txt
       - sphinx-build -b html docs public
     artifacts:
       paths: