I'm based in the US, where it's spelled without the "u". Quite a few examples of this spelling difference - humo(u)r, behavio(u)r etc. Oh and "spelt" is "spelled". Isn't English fun! :)
Even weirder, as a Native American English speaker, I would have spelt that word this way in only this context, but in other contexts it’s spelled this way.
Maybe this is my own idiosyncrasy though and not what others would do. I’ve never even thought about it until just now.