Fatal error: Class 'Facebook'

Let me tell you what happened when I updated your plugin from version 2.0.3 to 2.1.3 (thru WP panel).
While trying to log in with FB I get the following error:
Fatal error: Class ‘Facebook’ not found in /xxxx/xxxxx/xxxx/wp-content/plugins/wordpress-social-login/hybridauth/Hybrid/Providers/Facebook.php on line 36
PLEASE I need your help because I can’t go back to previous version and I’m stuck withe a live site.
Thanks, looking forward to your answer ASAP! I’m sure you understand my frustration and anxiety 🙂

http://ww.wp.xz.cn/extend/plugins/wordpress-social-login/