Update CI.yml

Author: fancaiyu

.github/workflows/CI.yml

@@ -39,7 +39,6 @@ jobs:
         run: |
           python -m pip install --upgrade pip
           pip install coverage
-          pip install sphinx
           pip install pytest
           pip install -r requirements.txt
 
@@ -64,6 +63,11 @@ jobs:
     steps:
       - uses: actions/checkout@v2
 
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install sphinx
+
       - name: Build documentation
         run: |
           cd docs