fix sign error in galactocentric matrix 1 [docs only]
fix sign error in galactocentric matrix 1 [docs only]

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