motor_support_l and motor_support_r wrong hole dimension

[Mitsuma]

Today while assembling my V-Core 3 I noticed that the CAD for the motor_support_l and motor_support_r parts have a small issue.

In the CAD the bigger diameter for the head of the screw shows 9.9mm for the M6 screw and 8.5mm for the M5 screw.
A DIN912 M6 screw has a diameter head of 10mm and 8.5mm for the M5 screw head.

So the bigger hole should be at least 10.2mm and 8.7mm diameter for the other for 0.2mm tolerance. (Maybe 10.3 and 8.8mm if 0.3mm tolerance was used.)

The lower hole for the thread is fine.

Im not comfortable in my CAD skills to make a pull request of my own changes, so I just post this issue here.