Filament Guide Lock Insert

Insert for [filboyt's Ender 3 Filament Guide Snap In](https://www.thingiverse.com/thing:2917932).

I am using the arm with a gap, and created this lock, to prevent the filament from getting away.

update (20180716):
I used Tony Buser's Pin Connectors V2 to add a locking mechanism, so it will not move.