Update .gitlab-ci.yml

.gitlab-ci.yml

@@ -14,6 +14,8 @@ pages:
   script:
     - apk --no-cache add py2-pip python-dev
     - pip install sphinx
+    - pip install sphinxcontrib-plantuml
+    - pip install sphinx-rtd-theme
     - apk --no-cache add make
     - cd docs
     - make html