Add node 8 to travis runs
Add node 8 to travis runs

Summary: Closes https://github.com/facebook/relay/pull/1837

Reviewed By: yuzhi

Differential Revision: D5152203

Pulled By: kassens

fbshipit-source-id: 0538a2ed6e5d63945ec36169239157b7d298df88

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