fix minor docs typo
fix minor docs typo

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