Merge pull request #4073 from gizmoguy/setup-cfg-py3.10

Add 3.10 support to setup.cfg.

Author: anarkiwi

setup.cfg

@@ -15,6 +15,7 @@ classifier =
     Programming Language :: Python :: 3.7
     Programming Language :: Python :: 3.8
     Programming Language :: Python :: 3.9
+    Programming Language :: Python :: 3.10
     Operating System :: Unix
 keywords =
     openflow