CFC: Fix "acknowledgment" in ACT Rules Format errata

Hey folks,

We are looking to do a small errata for the ACT Rules Format, where we're
changing the word "acknowledgement" to "acknowledgment". This changes the
spelling from British English to US English. This was discussed during last
week's call. You can find a pull request for this change here:

https://github.com/w3c/wcag-act/pull/443

This CFC lasts 48 hours, ending on Thursday April 2nd, 15:00 CET.

Kind regards,

-- 
*Wilco Fiers*
Axe for Web product owner - Co-facilitator WCAG-ACT - Chair ACT-R