How to close Server connection 
I have started a server connection to port 7000 in localhost with below code. Now how can I close this connection. 
```php
<?php
use Ratchet\Server\IoServer;
use MyApp\Chat;
    require dirname(__DIR__) . '/vendor/autoload.php';
    require dirname(__DIR__) . '/src/MyApp/Chat.php';

    $server = IoServer::factory(
        new Chat(), 
        7000
    );

    $server->run();
```