fix RelayFlowGenerator-test in OSS
fix RelayFlowGenerator-test in OSS

Summary:
Some difference with the babel setup changes how `...<generator>` works. This
avoids that issue by using `Array.from`.

Reviewed By: leebyron

Differential Revision: D4922886

fbshipit-source-id: b1b64655c48df65cd7125c8632616fccbd0840ce

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