doc typo fix
doc typo fix

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