Update astropy_helpers sub-module pointer to v0.4.2
Update astropy_helpers sub-module pointer to v0.4.2

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