fix for issue #10
fix for issue #10

pietro909/PhysicsJS,rohit765/PhysicsJS,VANITAX/PhysicsJS,Rawneed/PhysicsJS,Luwdo/PhysicsJS,mcanthony/PhysicsJS,griever989/PhysicsJS,eric-seekas/PhysicsJS,wellcaffeinated/PhysicsJS,wellcaffeinated/PhysicsJS,Nayar/PhysicsJS,eric-seekas/PhysicsJS,VANITAX/PhysicsJS,pietro909/PhysicsJS,131/PhysicsJS,Luwdo/PhysicsJS,mcanthony/PhysicsJS,haithemaraissia/PhysicsJS,aldeed/PhysicsJS,haithemaraissia/PhysicsJS,jpellerin/PhysicsJS,rohit765/PhysicsJS,Nayar/PhysicsJS,Rawneed/PhysicsJS,aldeed/PhysicsJS,griever989/PhysicsJS,jpellerin/PhysicsJS