improve the relay store doc by using the consistent imported name (#2665)
improve the relay store doc by using the consistent imported name (#2665)

Summary:
This part of the doc is very confusing, as you can see we import the pubic api in [L458](https://github.com/facebook/relay/pull/2665/files#diff-af6b98bdc4cbe6dedaed354e06c40bf4R458): `import {ConnectionHandler} from 'relay-runtime'` , but using `RelayConnectionHandler` in the rest of this page.

This patch change all of them to the imported one `ConnectionHandler`.
Pull Request resolved: https://github.com/facebook/relay/pull/2665

Differential Revision: D14280281

Pulled By: kassens

fbshipit-source-id: af939c720f369c22769adc1fa7c3f7676173fe3d

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