ignore gh-pages branch
ignore gh-pages branch

Summary:
Copied this trick from the Docusaurus repo to ignore gh-pages on CircleCI.
Closes https://github.com/facebook/relay/pull/2259

Differential Revision: D6661845

Pulled By: kassens

fbshipit-source-id: 10cf5ef73af00392091bec53fd4a3df561e5e9a4

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