Silence two warnings

Silence this just for the sandbox:

    [WARNING] You are not setting Devise.secret_key within your application!
    You must set this in config/initializers/devise.rb. Here's an example:

And silence this for everything using the Spree install generator:

    [deprecated] I18n.enforce_available_locales will default to true in the future. If you really want to skip validation of your locale you can set I18n.enforce_available_locales = false to avoid this message.