3Dator Bowden Extruder REMIXED (MK8 GEAR) base mod

A simple remix of the [3Dator Bowden Extruder REMIXED (MK8 GEAR)](http://www.thingiverse.com/thing:1679553) that adds a captive M5 nut to take the PC4-M5 push fitting for the PTFE tube. I've included the OpenSCAD file that I used to create the mod so anyone else could use it to create a base that takes a PC4-M6 fitting. This captive nut design is also used in the extruders of the Velleman Vertex K8400.