Fix function signature in docs.
Fix function signature in docs.

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