Register user security problem

I realized you can register new users using this plugin even if you set your WordPress to deny new users to do so.

I made a simple fix in user controller register method to make it follow your WordPress settings.

...
    public function register() {

        global $json_api;

        if (!get_option('users_can_register')) {
            $json_api->error("YOU CANNOT PASSS");            
        }
...