use isDefined method for OptionsResolver instead of isKnown
use isDefined method for OptionsResolver instead of isKnown

isKnown is deprecated since version 2.6

prolixtechnikos/LiipImagineBundle,liip/LiipImagineBundle,robfrawley/LiipImagineBundle,robfrawley/LiipImagineBundle,prolixtechnikos/LiipImagineBundle,liip/LiipImagineBundle,prolixtechnikos/LiipImagineBundle