can't distinguishing connection's close code
Hello, folks! I'm facing an issue while using cboden/ratchet v0.4.4. 

I'm having trouble distinguishing between 
```js
var conn = new WebSocket('ws://localhost:8088');
conn.close(4100, 'Abnormal closure')
```
and 
```js
conn.close(3100, 'whatelse') 
```
within the onClose(ConnectionInterface $conn) method. 

Thanks