middleware after graphql response

[crbonilha]

I perform an operation after my controller have sent their response, by calling the "next" callback.
The problem is the express-graphql doesn't receive nor call the "next" callback.

Is there a workaround this?
My suggestion is to have it receive the "next" parameter, and then if the user set a "callNext" option as true the "next" callback is called after the response is sent.

[vivekfyi]

Please check #279 . #374