Fix broken link to React example.
Fix broken link to React example.

Summary:This pull request updates the broken link to the React example in the documentation. It might be worthwhile to run [html-proofer](https://github.com/gjtorikian/html-proofer) on Travis builds to avoid broken links in the documentation in the future. I am more than happy to take a look at it if it sounds useful.

Fixes #1494.
Closes https://github.com/facebook/flow/pull/1496

Differential Revision: D3017232

Pulled By: jeffmo

fb-gh-sync-id: 921f0e65ee69f0d9834d3e7f82e993e37f01debf
shipit-source-id: 921f0e65ee69f0d9834d3e7f82e993e37f01debf

gabro/flow,popham/flow,chenglou/flow,gabro/flow,jeffmo/flow,jamesgpearce/flow,TiddoLangerak/flow,jeffmo/flow,graue/flow,mroch/flow,chenglou/flow,ForbesLindesay/flow,AprilArcus/flow,facebook/flow,nmote/flow,ForbesLindesay/flow,shiftcars/flow,d14b3l/flow,AprilArcus/flow,gabro/flow,jamesgpearce/flow,claudiopro/flow,fletcherw/flow,gabelevi/flow,claudiopro/flow,chenglou/flow,samwgoldman/flow,jdelStrother/flow,jeffmo/flow,cesarandreu/flow,jamesgpearce/flow,gabelevi/flow,nmote/flow,nmote/flow,AgentME/flow,graue/flow,ylu1317/flow,ForbesLindesay/flow,gabelevi/flow,nmote/flow,JonathanUsername/flow,facebook/flow,gabro/flow,ylu1317/flow,JonathanUsername/flow,jgrund/flow,d14b3l/flow,jdelStrother/flow,ForbesLindesay/flow,AgentME/flow,mroch/flow,AprilArcus/flow,fletcherw/flow,shiftcars/flow,ForbesLindesay/flow,samwgoldman/flow,graue/flow,jeffmo/flow,jgrund/flow,JonathanUsername/flow,samwgoldman/flow,popham/flow,d14b3l/flow,MichaelDeBoey/flow,nmote/flow,TiddoLangerak/flow,facebook/flow,popham/flow,mroch/flow,shiftcars/flow,samwgoldman/flow,MichaelDeBoey/flow,popham/flow,MichaelDeBoey/flow,TiddoLangerak/flow,fletcherw/flow,facebook/flow,AprilArcus/flow,gabro/flow,mroch/flow,jamesgpearce/flow,nmote/flow,gabelevi/flow,jgrund/flow,shiftcars/flow,AprilArcus/flow,AgentME/flow,jdelStrother/flow,mroch/flow,claudiopro/flow,jeffmo/flow,TiddoLangerak/flow,jgrund/flow,nmote/flow,mroch/flow,samwgoldman/flow,jdelStrother/flow,ylu1317/flow,jamesgpearce/flow,gabro/flow,d14b3l/flow,cesarandreu/flow,d14b3l/flow,d14b3l/flow,fletcherw/flow,chenglou/flow,jamesgpearce/flow,jgrund/flow,graue/flow,jdelStrother/flow,gabelevi/flow,facebook/flow,JonathanUsername/flow,jdelStrother/flow,MichaelDeBoey/flow,JonathanUsername/flow,MichaelDeBoey/flow,ylu1317/flow,mroch/flow,popham/flow,shiftcars/flow,fletcherw/flow,jamesgpearce/flow,TiddoLangerak/flow,facebook/flow,samwgoldman/flow,popham/flow,AgentME/flow,gabelevi/flow,AprilArcus/flow,AgentME/flow,fletcherw/flow,gabelevi/flow,JonathanUsername/flow,claudiopro/flow,shiftcars/flow,graue/flow,jeffmo/flow,ForbesLindesay/flow,chenglou/flow,ylu1317/flow,graue/flow,claudiopro/flow,popham/flow,cesarandreu/flow,chenglou/flow,cesarandreu/flow,JonathanUsername/flow,samwgoldman/flow,facebook/flow,jgrund/flow