Updating python version for CI docs. (#280)

MLCube uses mkdocs-click extension to automatically build web documentation pages for MLCube CLI. Theis library requires python version >= 3.7.

.github/workflows/docs-site.yml

@@ -14,7 +14,7 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v2
         with:
-          python-version: '3.6'
+          python-version: '3.8'
       - name: Install Python dependencies
         run: |
           python -m pip install --upgrade pip