response: #sendDate was forgotten

Hi,
Date response header is important but it was not provided.

Refs:
[RFC2616](http://www.ietf.org/rfc/rfc2616.txt)
[lib/\_http\_outgoing.js#L230](https://github.com/joyent/node/blob/master/lib/_http_outgoing.js#L230)
http://nodejs.org/api/http.html#http_response_senddate

Thanks.