remove oob, this is not supported in the API as the doc explains

Hey guys, I am trying my best to leave the Checkfront API code alone as I continue to develop. This issue was a little pain as this documentation says I should be able to use ```'redirect_uri' => 'oob'``` and pass the redirect_uri within the oAuth2 authentication process. 

As the docs states when using ```fetch_token($code)``` correctly it errors and will return the following error upon debugging the CURL request.

```Array ( [error] => redirect_uri_mismatch [error_description] => The redirect URI is missing or invalid )```

I looked over the doc and only see ```'redirect_uri' => 'oob'``` referenced once. Maybe is can be removed until the API code receives an update?