Pin React to 15.4
Pin React to 15.4

Summary:
React 15.5 adds a new warning which breaks a test. In order to fix it pin to the
working version of react until we fix the test.
Closes https://github.com/facebook/relay/pull/1594

Reviewed By: leebyron

Differential Revision: D4856463

Pulled By: kassens

fbshipit-source-id: b1f02657c131f786b4af481c4a14acac498d6109

atxwebs/relay,benjaminogles/relay,cpojer/relay,dbslone/relay,yungsters/relay,xuorig/relay,voideanvalue/relay,wincent/relay,atxwebs/relay,iamchenxin/relay,xuorig/relay,josephsavona/relay,apalm/relay,xuorig/relay,wincent/relay,kassens/relay,zpao/relay,atxwebs/relay,chentsulin/relay,wincent/relay,wincent/relay,iamchenxin/relay,kassens/relay,chirag04/relay,facebook/relay,kassens/relay,josephsavona/relay,voideanvalue/relay,kassens/relay,cpojer/relay,wincent/relay,facebook/relay,kassens/relay,rosskevin/relay,voideanvalue/relay,atxwebs/relay,chentsulin/relay,freiksenet/relay,chirag04/relay,yungsters/relay,voideanvalue/relay,facebook/relay,cpojer/relay,facebook/relay,iamchenxin/relay,josephsavona/relay,wincent/relay,zpao/relay,benjaminogles/relay,cpojer/relay,chentsulin/relay,voideanvalue/relay,kassens/relay,freiksenet/relay,facebook/relay,yungsters/relay,apalm/relay,zpao/relay,xuorig/relay,facebook/relay,freiksenet/relay,chirag04/relay,rosskevin/relay,xuorig/relay,apalm/relay,benjaminogles/relay,xuorig/relay,voideanvalue/relay,iamchenxin/relay,dbslone/relay