support mongoid 4.0.0
support mongoid 4.0.0

rrosenblum/bullet,sho-h/brakefast,flyerhzm/bullet,dwb/bullet,danp60/bullet,sideci-sample/sideci-sample-bullet,rstacruz/bullet,theass/bullet,eileencodes/bullet,yakovenkodenis/bullet,PikachuEXE/bullet,rstacruz/bullet,dwb/bullet,danp60/bullet,rrosenblum/bullet,hannahbot/bullet,eileencodes/bullet,jay3126/bullet,yakovenkodenis/bullet,flyerhzm/bullet,PikachuEXE/bullet,flyerhzm/bullet,sideci-sample/sideci-sample-bullet,theass/bullet,jay3126/bullet,sho-h/brakefast,hannahbot/bullet