Remove newline to satisfy setuptools (#4418)

Author: wjbenfold

setup.cfg

@@ -17,8 +17,7 @@ classifiers =
     Topic :: Scientific/Engineering
     Topic :: Scientific/Engineering :: Atmospheric Science
     Topic :: Scientific/Engineering :: Visualization
-description =
-    A powerful, format-agnostic, community-driven Python package for analysing and visualising Earth science data
+description = A powerful, format-agnostic, community-driven Python package for analysing and visualising Earth science data
 download_url = https://github.com/SciTools/iris
 keywords =
     cf-metadata