Add/Fix chartpress dependency ruamel.yaml

.github/workflows/chartpress.yaml

@@ -15,14 +15,14 @@ jobs:
     - name: Setup python
       uses: actions/setup-python@v2
       with:
-        python-version: '3.7'
+        python-version: '3.6'
 
     - name: Setup git
       run: git config --global user.email "[email protected]" && git config --global user.name "Github Action"
 
     - name: Install Chartpress
       run: |
-        pip install -v chartpress && pip install six
+        pip install -v chartpress && pip install six && pip install ruamel.yaml
     - name: Run Chartpress
       run: chartpress --push
       env: