Fix a small typo.
Fix a small typo.

[skip ci]

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