Add Python 3.9 to GitHub Actions / Workflows

Author: mdmintz

.github/workflows/python-package.yml

@@ -11,9 +11,9 @@ jobs:
 
     runs-on: ubuntu-18.04
     strategy:
-      max-parallel: 5
+      max-parallel: 6
       matrix:
-        python-version: [2.7, 3.5, 3.6, 3.7, 3.8]
+        python-version: [2.7, 3.5, 3.6, 3.7, 3.8, 3.9]
 
     steps:
     - uses: actions/checkout@v1