Fix CI

Author: kzosabe

.github/workflows/main.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [3.6, 3.9]
+        python-version: [3.7, 3.8, 3.9]
     steps:
       - name: Checkout
         uses: actions/checkout@v2