Add Python 3.10 to GitHub Actions test matrix (#280)

Co-authored-by: James Hilton-Balfe <[email protected]>

Author: kalzoo

.github/workflows/ci.yml

@@ -15,7 +15,7 @@ jobs:
     strategy:
       matrix:
         os: [Ubuntu, MacOS, Windows]
-        python-version: ['3.6.7', 3.7, 3.8, 3.9]
+        python-version: ['3.6.7', '3.7', '3.8', '3.9', '3.10']
         exclude:
           - os: Windows
             python-version: 3.6