Update Python versions on GitHub Actions

Author: fguillot

.github/workflows/ci.yml

@@ -13,7 +13,7 @@ jobs:
       max-parallel: 4
       matrix:
         os: [ubuntu-latest, windows-latest]
-        python-version: [3.6, 3.7, 3.8]
+        python-version: [3.8, 3.9]
 
     steps:
     - uses: actions/checkout@v1