VESC Speed Limit Params Control Opposite Limit

[palanc]

@romesco pointed out that vesc_driver/speed_min set in vesc/vesc_main/config/racecar_uw_nano/vesc.yaml limits how fast the car can move backwards, although it may be more intuitive for it to limit how fast it can move forwards. Similarly, vesc_driver/speed_max limits how fast the car can move backwards, but it might be more intuitive for it to control how fast it moves forwards. I believe that this mismatch is caused by the fact that the speed_to_erpm_gain is negative.