Fixing spelling errors in documentation

[Carl Sorensen]

John,

It's been brought to my attention that we are using an incorrect spelling
for "ukulele".  We've been using (at least in part of our documentation)
"ukelele".

I've done a git grep for ukelele, and found the misspelling existing in de/
es/ and fr/ notation/fretted-strings.itely.  I'm happy to fix it in all of
those, and I think I should do so.

I have read the CG, and I'm not sure if I should fix the misspelling in
Documentation/po/*.po.

If I do change the .po files, I think that I should allow the translations
meister to do the make *-update work.

Have I got it correct?

Thanks,

Carl