Lulzbot Mini 2 Corner Shim

corner shims to help with leveling the Lulzbot Mini 2 bed. Theoretically these shouldn't be necessary but after experiencing the same leveling issues described in [this thread](https://forum.lulzbot.com/t/solved-taz-6-auto-leveling-is-0-5mm-off-now-perfect-to-0-01mm/6250) I found that having shims helped a lot. These shims are the exact footprint of the bed corners, making it easier to get everything aligned.