v5.0.0
This version does not have any breaking changes. It's a major version as it has an automatic migration-step for the encryptionKey option. So if you're using that option, please continue reading.
Short story, Node.js deprecated the below APIs and we had to do encryption differently. Conf should be able to read both the new and old encryption format and it will write the new encryption format if you change any config. The migration is fully automatic, but please test your app thoroughly in case there are any issues.