Fix long-description in setup.cfg
[metadata]
name = gammapy
description = A Python package for gamma-ray astronomy
-long-descripton = file: LONG_DESCRIPTION.rst
+long-description = file: LONG_DESCRIPTION.rst
long-description-content-type = text/x-rst; charset=UTF-8
author = The Gammapy developers
author_email = gammapy@googlegroups.com
