chore: update comparisons.scad

[eltociear]

occurences -> occurrences

[amatulic]

If you're going to submit a fix for a typo, you might want to go through that file again to be sure you didn't miss others. For example, I found a couple cases of "approximately" misspelled with one "p".

Throughout other files, there's mixed usage of "toward" vs "towards" (the first is correct, but the latter seems more frequent here). There's also a lot of unnecessary future tense ("will" versus active-voice present-tense). Generally if I'm contributing code changes, I try to clean up the documentation at the same time, but it might be worthwhile to go through everything and make one big typo-correction PR, because the Wiki pages have to be rebuilt when the documentation in the comments changes.