Fixed typo in Group module docstring.
Fixed typo in Group module docstring.

grengojbo/grappelli-admin-tools-trunk,grengojbo/grappelli-admin-tools,grengojbo/grappelli-admin-tools,grengojbo/grappelli-admin-tools,grengojbo/grappelli-admin-tools-trunk,grengojbo/grappelli-admin-tools-trunk