Rathcore Bottle Cap Adapter

# I have developed a [better painting system](https://www.thingiverse.com/thing:4978320) and no longer use this. I got tired of keeping bottle caps around.

I really love the '.grip' bottle cap miniature holding system by [Aynareth](https://www.thingiverse.com/Aynareth), but I already own a few of the lovely miniature holders by [Rathcore](http://rathcore.com/miniature-holder/). So I created this remix to adapt the two together.