check exception class

I got this fatal error today : PHP Fatal error:  Call to undefined method Guzzle\Http\Exception\ServerErrorResponseException::getCurlHandle() in /home/frontoffice/instances/lekino-video_web/shared/vendor/guzzle/guzzle/src/Guzzle/Plugin/Backoff/BackoffPlugin.php on line 95
Merge pull request #451 from greg0ire/patch1

check exception class