Update gitlab-ci.yml.

.gitlab-ci.yml

@@ -2,9 +2,8 @@ image: alpine
 
 pages:
   script:
-  - apk --no-cache add py2-pip python-dev
-  - pip install -r requirements.txt
-  - pip install sphinx
+  - pip3 install -r requirements.txt
+  - pip3 install sphinx
   - apk --no-cache add make
   - cd docs && make html
   - mv build/html/ public/