Webhook json is sent in the body of the POST, not as a form parameter

The current example is not working: params is empty.
see: [https://developer.github.com/webhooks/creating/#content-type](https://developer.github.com/webhooks/creating/#content-type)

> “The application/json content type will deliver the JSON payload directly as the body of the POST”

And 

>  "For this tutorial, the default content type of application/json is fine"