How to cancel a scheduled email in mandrill?

I am using http://ift.tt/1DRHqds package to handle my emails in mandrill. The package has a method to schedule an email like this.

$timestamp = new DateTime('+1 hour');
$mandrill = MailTo::Mandrill();
$mandrill->addRecipient($email, $name)
         ->setFrom($email, $name)
         ->setHtml($html)
         ->setText($text)
         ->setSubject($subject)
         ->send($timestamp);

But I can't find a way to cancel a scheduled email. I read this docs http://ift.tt/1dMiZt6

Request JSON

 {
    "key": "example key",
    "id": null
} 

but I don't know how to implement this. Does anyone can help me with this?