fix deprecated escape sequence in ascii read documentation [skip ci]
fix deprecated escape sequence in ascii read documentation [skip ci]

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