Try running CI with python 3.7.14

.github/workflows/coverage.yml

@@ -18,7 +18,7 @@ jobs:
       - name: Install Python
         uses: actions/setup-python@v2
         with:
-          python-version: 3.5
+          python-version: 3.7.14
       - name: Install covimerage
         run: |
           pip install covimerage