Fix issue where accessKey isn't passed into client config

[joshgillies]

I might be missing something but the docs suggest the following snippet should work:

var client = sdk.createClient({
  accessKey: 'private-key'
})

However the private key doesn't get sent with requests, and thus requests aren't authenticated. The patch here fixes this.

---

As a work around this currently behaves as expected:

var client = sdk.createClient({
  hook_private_key: 'private-key'
})