Update res.end([data] [, encoding])

[bjohansebas]

This method accepts a callback, which was added in Node version 0.11.6, making it compatible with both Express v4 and v5.

There is probably a backport to Node.js 0.8, but I'm not sure.

ref:

• https://nodejs.org/api/http.html#requestenddata-encoding-callback
• https://nodejs.org/en/blog/release/v0.11.6/
• response.end() proxy does not accept callback parameter session#477

[axhuwastaken]

#1719