Fix incorrect example in docs; fixes #3079 [skip ci]
Fix incorrect example in docs; fixes #3079 [skip ci]

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