[PR] Fix redeclaration error in docs
[PR] Fix redeclaration error in docs

Summary:
Fixes this error:

![image](https://user-images.githubusercontent.com/415057/40847723-2538ba08-658b-11e8-805c-a72eb50c124c.png)
Closes https://github.com/facebook/flow/pull/6406

Reviewed By: fishythefish

Differential Revision: D8285658

Pulled By: mrkev

fbshipit-source-id: 45b15950d358943bc2fb563b21981ec759bf50f3

facebook/flow,mroch/flow,facebook/flow,popham/flow,facebook/flow,AgentME/flow,samwgoldman/flow,gabelevi/flow,JonathanUsername/flow,jamesgpearce/flow,facebook/flow,mroch/flow,AgentME/flow,JonathanUsername/flow,facebook/flow,jamesgpearce/flow,AgentME/flow,claudiopro/flow,nmote/flow,nmote/flow,JonathanUsername/flow,jamesgpearce/flow,claudiopro/flow,nmote/flow,gabelevi/flow,gabelevi/flow,nmote/flow,jamesgpearce/flow,mroch/flow,nmote/flow,jamesgpearce/flow,samwgoldman/flow,JonathanUsername/flow,samwgoldman/flow,samwgoldman/flow,gabelevi/flow,facebook/flow,samwgoldman/flow,JonathanUsername/flow,claudiopro/flow,gabelevi/flow,claudiopro/flow,popham/flow,gabelevi/flow,jamesgpearce/flow,nmote/flow,mroch/flow,nmote/flow,popham/flow,JonathanUsername/flow,mroch/flow,claudiopro/flow,popham/flow,facebook/flow,mroch/flow,mroch/flow,samwgoldman/flow,popham/flow,AgentME/flow,gabelevi/flow,jamesgpearce/flow,popham/flow,samwgoldman/flow,AgentME/flow,JonathanUsername/flow,popham/flow