Typo in the documentation

I think in this example second function must be decorated with `@sio.on('leave room')` instead of `@sio.on('enter room')`.

```
@sio.on('enter room')
def enter_room(sid, data):
    sio.enter_room(sid, data['room'])

@sio.on('enter room')
def leave_room(sid, data):
    sio.leave_room(sid, data['room'])
```
