Update python versions for unit testing (#52)

[3.5, 3.6, 3.7, 3.8] -> [3.7, 3.8, 3.9, 3.10]

Author: karolzak

.github/workflows/python-package.yml

@@ -15,7 +15,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
-        python-version: [3.5, 3.6, 3.7, 3.8]
+        python-version: ["3.7", "3.8", "3.9", "3.10"]
 
     steps:
     - uses: actions/checkout@v2