Fix creation of column mask in example.
Fix creation of column mask in example.

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