BLTouch mount with recessed M3 nut for Bullseye fan duct

This is a modded holder for the BLTouch that can be used together with the Petsfang Bullseye fan duct on Creality CR-10, CR-20 and Ender 3.

Changes:

- recess for M3 nuts (since I grew tired of the screws coming loose every now and then) also beefed up the edges around so it wont break around these nuts.
- Increased clearance between BLTouch mount and fan duct (easier to install)