fix examples now that frame attribute default is None [docs only]
fix examples now that frame attribute default is None [docs only]

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