minor edit to readme
minor edit to readme

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