Mosaic Z endstop support.

After about two months of owning a MakerGear Mosaic, I had only one small issue. The guide rod that the Z-endstop is attached to could rotate freely, causing the endstop switch to move out of place with the vibrations of the printer.

This is a simple modification to the original Z-endstop that ships with the Mosaic to keep the guide rod from rotating.