DOC: Remove groupby from flake8-rst section exclusions (redo after merge with master)

Author: LJArendse

setup.cfg

@@ -53,7 +53,6 @@ exclude =
     doc/source/basics.rst
     doc/source/contributing_docstring.rst
     doc/source/enhancingperf.rst
-    doc/source/groupby.rst
 
 
 [yapf]