add python 3.10 to python-ci

Author: kp-cat

.github/workflows/python-ci.yml

@@ -17,7 +17,7 @@ jobs:
     runs-on: ubuntu-18.04
     strategy:
       matrix:
-        python-versions: [2.7, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9]
+        python-versions: ["2.7", "3.3", "3.4", "3.5", "3.6", "3.7", "3.8", "3.9", "3.10"]
 
     steps:
     - uses: actions/checkout@v2