Add Py 3.9 to CI (#27)

Author: TheTripleV

.github/workflows/workflow.yml

@@ -26,7 +26,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ['3.6', '3.7',  '3.8', 'pypy3']
+        python-version: ['3.6', '3.7',  '3.8', '3.9', 'pypy3']
     steps:
       - uses: actions/checkout@v2
       - name: Setup Python