JWT-Token: Class 'Tymon\JWTAuth\Providers\JWTAuthServiceProvider' not found

I'm using this guide http://ift.tt/1Pr7W6s to implement JWT-token, but when I come to the section where I want to test my API i get this error:

Class 'Tymon\JWTAuth\Providers\JWTAuthServiceProvider' not found

No matter which route I try to access this error pops up. I'm quite new at laravel so I can't figure out what is wrong, or what I'm not doing right - Thank you.

via Chebli Mohamed