Minor fix in mutation doc
Minor fix in mutation doc

Reviewed By: dwwoelfel

Differential Revision: D5883439

fbshipit-source-id: 9820cf3f82310082c546f5bd0dfaa81cfb25a3ec

yungsters/relay,wincent/relay,benjaminogles/relay,xuorig/relay,wincent/relay,facebook/relay,voideanvalue/relay,xuorig/relay,cpojer/relay,kassens/relay,cpojer/relay,atxwebs/relay,kassens/relay,zpao/relay,xuorig/relay,wincent/relay,josephsavona/relay,freiksenet/relay,xuorig/relay,wincent/relay,freiksenet/relay,yungsters/relay,voideanvalue/relay,iamchenxin/relay,voideanvalue/relay,zpao/relay,kassens/relay,facebook/relay,facebook/relay,wincent/relay,facebook/relay,xuorig/relay,zpao/relay,josephsavona/relay,benjaminogles/relay,benjaminogles/relay,apalm/relay,atxwebs/relay,xuorig/relay,kassens/relay,voideanvalue/relay,facebook/relay,atxwebs/relay,cpojer/relay,wincent/relay,cpojer/relay,apalm/relay,apalm/relay,iamchenxin/relay,yungsters/relay,facebook/relay,freiksenet/relay,iamchenxin/relay,dbslone/relay,kassens/relay,josephsavona/relay,atxwebs/relay,voideanvalue/relay,voideanvalue/relay,iamchenxin/relay,dbslone/relay,kassens/relay