The NEC does not allow the device (receptacle) to bond the box. Since the MC sheath is not rated for grounding, you must ground the green wire to the box. Here we use a green wire pigtail that comes with a #10 screw available a most any supply house. This screws to the tapped ground screw hole in the box. We use a special green wirenut with a hole in it that allows the green wire to be stripped out bare long enough to reach the receptacle after it leaves the wirenut.