Fix deprecated/invalid setup.cfg

Dash-separated keys for setuptools config have been deprecated in [v54.1.10 (2021)](https://setuptools.pypa.io/en/latest/history.html#id855)and removed in [v78](https://setuptools.pypa.io/en/latest/history.html#v78-0-0).

Author: abravalheri

setup.cfg

@@ -2,7 +2,7 @@
 universal = 1
 
 [metadata]
-description-file = README.md
+description_file = README.md
 license = MIT
 
 [flake8]