Use requirements.txt in gitlab CI config

.gitlab-ci.yml

@@ -7,7 +7,7 @@ stages:
 build lectures:
   stage: build
   before_script:
-    - pip install -U mkdocs mkdocs-material python-markdown-math notedown
+    - pip install -Ur requirements.txt
   script:
     - python execute.py
     - mkdocs build