Mephisto Drax (version 0.8) introduces breaking changes for plugins. I've just finished updating the contact / feedback form plugin. It's now working fine and tests passing.
Installation instructions are the same as before except that the 'contact_notifier' has moved from the 'lib' directory to the 'app' directory. It still needs to be updated to include your destination email address for contact mails.
If you're a Mephisto plug-in developer, you might be interested in checking out my post on migrating Mephisto plugins to Drax. It's based on my experiences with the contact_form.