Correct a typo in stream docs.

lib/websocket/streams.js

@@ -121,7 +121,7 @@ Messages.prototype.write = function(message) {
   return !this._paused;
 };
 
-// The Messages end() method will be caused when a stream piping into it emits
+// The Messages end() method will be called when a stream piping into it emits
 // 'end'. Many streams may be piped into the WebSocket and one of them ending
 // does not mean the whole socket is done, so just process the input and move
 // on leaving the socket open.