fixed typo in the triangle_difference_v() function

[d4v3y5c0n3s]

For the "max" variable, ".x" was used when it should have been ".y".

Please let me know if you have any questions about this fix.

[blogdron]

Yes I think this is a just copy-paste bug =) This function hasn't been used anywhere, so the fix won't break anything.

[orangeduck]

Thanks!