Fix version to 3.7

Author: pawks

.github/workflows/main.yml

@@ -31,7 +31,7 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v2
         with:
-          python-version: '3.6.15'
+          python-version: '3.7'
 
       - name: Install dependencies
         run: |