Typo in BOMfor 500mm Variant

[bhannawa]

Check the link here to see the problem for yourself. Two sections are titled "400mm panel set." The second title should say "500mm panel set."
https://v-core.ratrig.com/bom/#v-core-3-enclosure-400mm-panel-set-polycarbonate-4mm-hw2780gk_1

[oneredstar]

I found this issue as well as I was prepping to make the panels. Raised a PR for convenience.

#66