Let's go with `ensure_confirmation_token!` because that's [the API we use in token authenticatable](https://github.com/plataformatec/devise/blob/master/lib/devise/models/token_authenticatable.rb#L63).

Also, we can change [this line](https://github.com/sslotnick/devise/blob/b5909f9b936078416732bf1d84b0fb8692e9cdff/lib/devise/models/confirmable.rb#L96) to use this new method. :)