Bug: Does not quit cleanly

I don't think it's ever exited cleanly for me. I always have to hit Ctrl+C twice to exit:

```
$ obfuscation-tunnel -l udp:0.0.0.0:12345 -r udp:192.168.2.1:58223
Started UDP server at 0.0.0.0:12345
Started UDP client for 192.168.2.1:58223
^CExiting...
^CKilled
```