fix py 2.x incompatibility
fix py 2.x incompatibility

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