MMU2 filament buffer with holes

Remix of bottom parts of https://www.prusaprinters.org/prints/3292-mmu2-filament-buffer/files.

Original parts are a really good solution for the buffer filament, but lack of stability on the LACK V2 enclosure (for example with the top opening).
So, I just replaced the "dome" polygon on each bottom side by a hole, to be able to screw the parts (with 5x20 screws) on the LACK table.

Print instructions

Same as original part.
Screwing only one part should be OK to secure the buffer.