hangup
To make the bot to end the call, use the hangup reply type.
Supported in the phone channel only.
tip
You can also use the equivalent 
$dialer.hangUp method.Syntax
$response.replies.push({"type": "hangup"});
How to use
state: EndCall
    a: Have a nice day!
    script:
        $response.replies = $response.replies || [];
        $response.replies.push({"type": "hangup"});