MailView not defined in prod

[vfonic]

Hi!

I tried to deploy my newly created app and the failure error was that MailView is undefined. This is due to mail_view gem being available in group :development only, which makes sense. I'm not sure what would be the best way to have this working so that we can still keep this:
https://github.com/RailsApps/rails_apps_composer/blob/master/recipes/email_dev.rb#L44