install deps on deploy

If the requirements.txt is changed in the repo, the new dependencies need to be installed on the production server.
This didn't happen with #106 hence the fix didn't affect the actual docs page.

.github/workflows/deploy.yml

@@ -12,6 +12,10 @@ jobs:
 
     steps:
     - uses: actions/checkout@v2
+    - name: Install Dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install -r requirements.txt
     - name: Deploy to server
       id: deploy
       uses: Pendect/[email protected]