fix footprint docstring
fix footprint docstring

kelle/astropy,joergdietrich/astropy,bsipocz/astropy,MSeifert04/astropy,DougBurke/astropy,lpsinger/astropy,AustereCuriosity/astropy,saimn/astropy,MSeifert04/astropy,joergdietrich/astropy,kelle/astropy,saimn/astropy,DougBurke/astropy,lpsinger/astropy,bsipocz/astropy,stargaser/astropy,pllim/astropy,bsipocz/astropy,AustereCuriosity/astropy,joergdietrich/astropy,dhomeier/astropy,larrybradley/astropy,astropy/astropy,funbaker/astropy,StuartLittlefair/astropy,aleksandr-bakanov/astropy,StuartLittlefair/astropy,saimn/astropy,dhomeier/astropy,saimn/astropy,larrybradley/astropy,larrybradley/astropy,joergdietrich/astropy,astropy/astropy,lpsinger/astropy,DougBurke/astropy,bsipocz/astropy,mhvk/astropy,AustereCuriosity/astropy,funbaker/astropy,pllim/astropy,aleksandr-bakanov/astropy,tbabej/astropy,saimn/astropy,larrybradley/astropy,dhomeier/astropy,funbaker/astropy,joergdietrich/astropy,DougBurke/astropy,stargaser/astropy,aleksandr-bakanov/astropy,mhvk/astropy,mhvk/astropy,pllim/astropy,pllim/astropy,MSeifert04/astropy,larrybradley/astropy,tbabej/astropy,StuartLittlefair/astropy,tbabej/astropy,mhvk/astropy,aleksandr-bakanov/astropy,funbaker/astropy,tbabej/astropy,StuartLittlefair/astropy,AustereCuriosity/astropy,lpsinger/astropy,AustereCuriosity/astropy,tbabej/astropy,StuartLittlefair/astropy,kelle/astropy,mhvk/astropy,kelle/astropy,kelle/astropy,stargaser/astropy,astropy/astropy,lpsinger/astropy,astropy/astropy,dhomeier/astropy,MSeifert04/astropy,astropy/astropy,pllim/astropy,dhomeier/astropy,stargaser/astropy