stream: fix incorrect comment in _stream_readable.js

PR-URL: #19882
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/_stream_readable.js

@@ -302,7 +302,7 @@ function chunkInvalid(state, chunk) {
 }
 
 
-// if it's past the high water mark, we can push in some more.
+// We can push more data if we are below the highWaterMark.
 // Also, if we have no data yet, we can stand some
 // more bytes.  This is to work around cases where hwm=0,
 // such as the repl.  Also, if the push() triggered a