Restore .gitlab-ci.yml file

.gitlab-ci.yml

@@ -10,8 +10,7 @@ build lectures:
     - pip install -U mkdocs mkdocs-material python-markdown-math notedown
   script:
     - python execute.py
-    - mkdocs build --clean
-    - mkdocs serve
+    - mkdocs build
   artifacts:
     paths:
       - site