doc: improve http.abort description

Per #4409, the documentation on http.abort is a bit lacking.
This provides a slight improvement.

Reviewed-By: James M Snell <jasnell@gmail.com>
PR-URL: nodejs/node-v0.x-archive#25591

Author: jasnell

doc/api/http.markdown

@@ -897,7 +897,8 @@ is finished.
 
 ### request.abort()
 
-Aborts a request.  (New since v0.3.8.)
+Marks the request as aborting. Calling this will cause remaining data
+in the response to be dropped and the socket to be destroyed.
 
 ### request.setTimeout(timeout[, callback])