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
14b3aab7d289a568e4a9efa6cd07a6ced370e318:

    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: https://github.com/nodejs/node/pull/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

@@ -519,7 +519,7 @@ 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.
@@ -1900,6 +1900,7 @@ const req = http.request(options, (res) => {
 [`net.createConnection()`]: net.html#net_net_createconnection_options_connectlistener
 [`request.socket`]: #http_request_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.socket`]: #http_response_socket