closing connection manually does not trigger onClose
### What I've figured out so far

1. The connection is reported to be closed for client with the same 1010 code, so it actually gets closed and no problem on that side.
2. If the connection is closed by the client, this function gets triggered without any problems.

### The problem
I'm doing something like:

```php
$conn->close(1010);
```

But this function is not triggered.
```php
    public function onClose( ConnectionInterface $conn ) {
        $this->print("ssss");
        parent::onClose( $conn );
    }
```

I use that function to cleanUp connection specific data, so it's kind of important.
however I can just call it myself, but I need to know is this a bug or is it intended? (to prevent duplication.)


Also using :

```php
        $ws_server->enableKeepAlive($server->loop, 15);
```

Not sure if that is supposed to help in this case, but it has no effect on this case.