Cable Clip 4mm cable retainer

This part acts as a cable retainer insert for the [Cable Clip](http://www.thingiverse.com/thing:1940480) by [rp21](http://www.thingiverse.com/rp21/about). There are four 4mm openings which fit the Lightning and USB cables I have tested, and keeps them from falling through while allowing them to be freely extended through the body of the Cable Clip.