doc: improve httpVersionMajor / httpVersionMajor

The description of httpVersionMajor & httpVersionMinor should
have same context like httpVersion.

PR-URL: https://github.com/nodejs/node/pull/5296
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>

doc/api/http.markdown

@@ -891,8 +891,8 @@ In case of server request, the HTTP version sent by the client. In the case of
 client response, the HTTP version of the connected-to server.
 Probably either `'1.1'` or `'1.0'`.
 
-Also `response.httpVersionMajor` is the first integer and
-`response.httpVersionMinor` is the second.
+Also `message.httpVersionMajor` is the first integer and
+`message.httpVersionMinor` is the second.
 
 ### message.method