Use setup.cfg for tox configuration

Author: Harmon758

setup.cfg

@@ -5,3 +5,10 @@ source = tweepy
 omit =
     */python?.?/*
     */site-packages/*
+
+[tox:tox]
+envlist = py37, py38, py39, py310
+
+[testenv]
+commands = python -m unittest discover tests
+extras = test