doc: fix mistake in http.md

If the first parameter of `request.end` `data` is specified, it should
be equivalent to calling `request.write(data, encoding)` (not
`response.write(data, encoding)`) followed by `request.end(callback)`.

This mistake was introduced in commit
14b3aab:

    date: 28 November 2015 at 7:30:32 AM GMT+8
    author: jpersson <jonathan.persson@creuna.se>
    committer: James M Snell <jasnell@gmail.com>
    summary: doc: add links and backticks around names

PR-URL: #14126
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: David Cai <davidcai1993@yahoo.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>

doc/api/http.md

@@ -474,7 +474,7 @@ unsent, it will flush them to the stream. If the request is
 chunked, this will send the terminating `'0\r\n\r\n'`.
 
 If `data` is specified, it is equivalent to calling
-[`response.write(data, encoding)`][] followed by `request.end(callback)`.
+[`request.write(data, encoding)`][] followed by `request.end(callback)`.
 
 If `callback` is specified, it will be called when the request stream
 is finished.
@@ -1670,6 +1670,7 @@ There are a few special headers that should be noted.
 [`net.Server.listen(port)`]: net.html#net_server_listen_port_hostname_backlog_callback
 [`net.Socket`]: net.html#net_class_net_socket
 [`request.socket.getPeerCertificate()`]: tls.html#tls_tlssocket_getpeercertificate_detailed
+[`request.write(data, encoding)`]: #http_request_write_chunk_encoding_callback
 [`response.end()`]: #http_response_end_data_encoding_callback
 [`response.setHeader()`]: #http_response_setheader_name_value
 [`response.write()`]: #http_response_write_chunk_encoding_callback