Add environment argument to mutation example
Add environment argument to mutation example

Summary:
When copying the example mutation I found that the `environment` variable was not present. I looked at the Todo example, https://github.com/relayjs/relay-examples/blob/master/todo-modern/js/mutations/AddTodoMutation.js#L51,  and a few other implementations and all seem to pass it as the first argument to the mutation. 😄
Closes https://github.com/facebook/relay/pull/2002

Differential Revision: D5806764

Pulled By: leebyron

fbshipit-source-id: de5033805d76b9d70851d6f0cf90afded58451be

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