There is no donation button/link because the Carbonite developers/authors have removed it.
Carbonite has its' own forums, and this question probably would have been better asked there instead of the "General WoW Chat" forum, simply because a lot of folks wouldn't have any idea at all what "downloaded the new version (5.041)" refers to.
You can access Carbonites forums by hovering the "Forums" link at the top of any WoWI page, then Categories, and clicking on Featured Projects and picking one of the Carbonite forums listed there. You can also access them by going HERE and clicking the "Forums" link in the navigation bar. There is also a link to them on the information page for Carbonite here on WoWI.
Ahhhh, the vagueries of the aging mind. Wait.... What was I saying?