Modified Promega rear cable chain mount

This is a remix of the rear cable chain mount for the M3D Promega printer. The original is posted in the Promega Public Google Drive, linked on the Promega support site: http://promega.printm3d.com.

You will need an M3x25mm flat head screw and an M3 heat insert in addition to reusing the chain attachment and M5 anchor hardware.

The following improvements were made:

1. The "bridge" above the motor mounting screw now has a vertical slot to allow a thin screwdriver to be used on the screw