fix mask bug
fix mask bug

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