Map command to [0,1] interval

Right now, the close command is not 1, but the value computed here:
https://github.com/beta-robots/robotiq/blob/new_2_finger_models/robotiq_2f_hw_usb/include/robotiq_2f_hw_usb/robotiq_2f_usb_comm.h#L24

This comes from the URDF conversion to uint8 type here:
https://github.com/beta-robots/robotiq/blob/new_2_finger_models/robotiq_2f_hw_usb/include/robotiq_2f_hw_usb/robotiq_2f_usb_comm.h#L51