Minor typos in `docs/modeling/new.rst`
Minor typos in `docs/modeling/new.rst`

A few very minor typos I encountered while reading the docs.
MSeifert04/astropy,astropy/astropy,StuartLittlefair/astropy,mhvk/astropy,larrybradley/astropy,kelle/astropy,funbaker/astropy,DougBurke/astropy,astropy/astropy,aleksandr-bakanov/astropy,astropy/astropy,joergdietrich/astropy,kelle/astropy,aleksandr-bakanov/astropy,AustereCuriosity/astropy,stargaser/astropy,dhomeier/astropy,stargaser/astropy,DougBurke/astropy,saimn/astropy,bsipocz/astropy,tbabej/astropy,StuartLittlefair/astropy,saimn/astropy,larrybradley/astropy,AustereCuriosity/astropy,bsipocz/astropy,joergdietrich/astropy,kelle/astropy,kelle/astropy,bsipocz/astropy,funbaker/astropy,kelle/astropy,AustereCuriosity/astropy,aleksandr-bakanov/astropy,lpsinger/astropy,lpsinger/astropy,joergdietrich/astropy,DougBurke/astropy,stargaser/astropy,astropy/astropy,saimn/astropy,dhomeier/astropy,tbabej/astropy,MSeifert04/astropy,pllim/astropy,dhomeier/astropy,MSeifert04/astropy,tbabej/astropy,stargaser/astropy,pllim/astropy,lpsinger/astropy,AustereCuriosity/astropy,pllim/astropy,lpsinger/astropy,AustereCuriosity/astropy,pllim/astropy,funbaker/astropy,pllim/astropy,larrybradley/astropy,mhvk/astropy,astropy/astropy,tbabej/astropy,bsipocz/astropy,funbaker/astropy,mhvk/astropy,joergdietrich/astropy,aleksandr-bakanov/astropy,saimn/astropy,dhomeier/astropy,StuartLittlefair/astropy,mhvk/astropy,dhomeier/astropy,MSeifert04/astropy,lpsinger/astropy,larrybradley/astropy,mhvk/astropy,StuartLittlefair/astropy,larrybradley/astropy,DougBurke/astropy,joergdietrich/astropy,tbabej/astropy,StuartLittlefair/astropy,saimn/astropy