Add Python 3.10 to tox.ini
diff --git a/tox.ini b/tox.ini
index 0d60804..d736a6c 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-envlist = pypy3,py36,py37,py38,py39
+envlist = pypy3,py36,py37,py38,py39,py310
 
 [testenv]
 deps =