Build the Relay Playground in DEV mode.
Build the Relay Playground in DEV mode.

Summary: Closes https://github.com/facebook/relay/pull/726

Reviewed By: yungsters

Differential Revision: D2812206

fb-gh-sync-id: b29c23383f16202ef72aea656e4721d14b16a72f

cpojer/relay,wincent/relay,atxwebs/relay,mroch/relay,NevilleS/relay,atxwebs/relay,atxwebs/relay,cpojer/relay,benjaminogles/relay,facebook/relay,rosskevin/relay,josephsavona/relay,wincent/relay,facebook/relay,voideanvalue/relay,mroch/relay,Aweary/relay,NevilleS/relay,facebook/relay,zpao/relay,kassens/relay,benjaminogles/relay,chirag04/relay,chentsulin/relay,wincent/relay,voideanvalue/relay,xuorig/relay,venepe/relay,apalm/relay,yungsters/relay,freiksenet/relay,cesarandreu/relay,forter/generic-relay,dbslone/relay,facebook/relay,zpao/relay,voideanvalue/relay,wincent/relay,mroch/relay,xuorig/relay,iamchenxin/relay,freiksenet/relay,chirag04/relay,michaelchum/relay,NevilleS/relay,dbslone/relay,xuorig/relay,Aweary/relay,yungsters/relay,iamchenxin/relay,josephsavona/relay,chentsulin/relay,cpojer/relay,voideanvalue/relay,cpojer/relay,xuorig/relay,voideanvalue/relay,apalm/relay,andimarek/generic-relay,gabelevi/relay,cesarandreu/relay,voideanvalue/relay,gabelevi/relay,zpao/relay,chirag04/relay,facebook/relay,freiksenet/relay,rosskevin/relay,atxwebs/relay,facebook/relay,iamchenxin/relay,gabelevi/relay,benjaminogles/relay,kassens/relay,josephsavona/relay,wincent/relay,xuorig/relay,andimarek/generic-relay,venepe/relay,xuorig/relay,chentsulin/relay,apalm/relay,yungsters/relay,andimarek/generic-relay,kassens/relay,wincent/relay,michaelchum/relay,iamchenxin/relay,kassens/relay,kassens/relay,venepe/relay,michaelchum/relay,kassens/relay,cesarandreu/relay,Aweary/relay