Fixes deprecation warning for Express 4.x send()

In `Express.js` versions after `4.x`, specifying the HTTP response status code as first argument of the `send()` method is deprecated.
Where before you would've had the following piece of code:

`response.send(200, 'Hello World!');`

you now have:

`response.status(200).send('Hello World!');`

Although the specs use `Express.js` in versions 3.x, the change I made is backwards-compatible.

This pull-request fixes this problem in both the webhooks file and the specs.
I ran the test suite on my computer and they all passed without an issue.