The gem hasn't been upgraded to support Rails 4.2. We've tried the https://github.com/safetypins/vestal_versions fork but it fails when attempts are made to destroy objects (see #111 (comment)).
We're considering moving from Vestal Versions to PaperTrail. However, if Vestal Versions was to be updated to support Rails 4.2 we may reconsider.
@laserlemon @midas @dreamr what are your intentions for Vestal Versions? Do you intend to continue maintaining it?