Bug in organizations support

Using php-chef with organizations, not all url endpoints must have /organizations/organization_name,
If you try to check server status
https://docs.chef.io/api_chef_server.html#status
It must be done using http://server/_status
But php-chef is using
http://server/organizations/org_name/_status
which causes an error.

To reproduce, just test as:

```
$chef = new Jenssegers\Chef\Chef(https://chef_server/organizations/my_organization", 'my_username', 'key_path', "12.0.1", TRUE);
$chef->get('/_status');
```