Sender.Hixie ignores the fin flag

[kersam-bl]

The Sender.Hixie's send() method simply ignores the fin flag.
This leads to incomplete frames when using Websockets.stream() or send() with a read stream.
Suggested fix:
Write the final FF byte only when fin === true, write the initial 00 byte only when the last frame was terminated.

[einaros]

I've included a fix for this in the latest release, which will be pushed soon. Thank you!