Update .gitlab-ci.yml file

.gitlab-ci.yml

 stages:
-  - build
+  - build1
+  - build2
   - deploy
 
 variables:
@@ -11,7 +12,7 @@ cache:
     - venv/
 
 jupyter-build-html:
-  stage: build
+  stage: build1
   image: jupyter/scipy-notebook
   script:
     - python3 -V  # Print out python version for debugging
@@ -28,7 +29,7 @@ jupyter-build-html:
       - _build/
 
 jupyter-build-pdf:
-  stage: build
+  stage: build2
   image: sphinxdoc/sphinx-latexpdf
   script:
     - python3 -V  # Print out python version for debugging