[PR] Grammar fix.
[PR] Grammar fix.

Summary: Closes https://github.com/facebook/flow/pull/3494

Differential Revision: D4785678

Pulled By: mroch

fbshipit-source-id: 00250bc4c0b1b5136d1c5c3d598b62af12700f4a

JonathanUsername/flow,mroch/flow,mroch/flow,TiddoLangerak/flow,popham/flow,facebook/flow,gabro/flow,claudiopro/flow,MichaelDeBoey/flow,samwgoldman/flow,samwgoldman/flow,claudiopro/flow,claudiopro/flow,JonathanUsername/flow,samwgoldman/flow,popham/flow,ylu1317/flow,jamesgpearce/flow,claudiopro/flow,mroch/flow,AgentME/flow,MichaelDeBoey/flow,ylu1317/flow,gabelevi/flow,jamesgpearce/flow,AgentME/flow,ylu1317/flow,MichaelDeBoey/flow,facebook/flow,nmote/flow,gabro/flow,facebook/flow,AgentME/flow,popham/flow,nmote/flow,gabelevi/flow,gabelevi/flow,nmote/flow,gabro/flow,gabelevi/flow,gabro/flow,nmote/flow,facebook/flow,nmote/flow,jamesgpearce/flow,facebook/flow,mroch/flow,popham/flow,JonathanUsername/flow,jamesgpearce/flow,jamesgpearce/flow,TiddoLangerak/flow,JonathanUsername/flow,JonathanUsername/flow,fletcherw/flow,fletcherw/flow,AgentME/flow,samwgoldman/flow,jamesgpearce/flow,samwgoldman/flow,gabelevi/flow,fletcherw/flow,ylu1317/flow,JonathanUsername/flow,nmote/flow,popham/flow,popham/flow,MichaelDeBoey/flow,nmote/flow,claudiopro/flow,mroch/flow,jamesgpearce/flow,samwgoldman/flow,fletcherw/flow,fletcherw/flow,mroch/flow,TiddoLangerak/flow,ylu1317/flow,samwgoldman/flow,facebook/flow,TiddoLangerak/flow,popham/flow,MichaelDeBoey/flow,JonathanUsername/flow,gabro/flow,fletcherw/flow,gabelevi/flow,AgentME/flow,TiddoLangerak/flow,gabelevi/flow,gabro/flow,facebook/flow,mroch/flow