Chang max username lenght to 16

I think you should change the username lenght to 16, else you get kicked with the following exception: 

```
Internal exception: java.io.IOException: Received string length longer than maximum allowed (18 > 16)
```

You changed it in [this](https://github.com/Howaner/FakeMobs/commit/ffa5449f788dcbdfab00d7b5752f00331eb14a6e) commit to 32 characters.
