Check with stable Python 3.10 (#902)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 7ccde29..70c69cf 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -14,7 +14,7 @@
     strategy:
       fail-fast: false
       matrix:
-        python-version: [3.10-dev, 3.9, 3.8, 3.7, 3.6]
+        python-version: ["3.6", "3.7", "3.8", "3.9", "3.10"]
 
     runs-on: ubuntu-latest