title: Carrierwave doesn't recreate versions after the model update
body: <p>I've introduced a new version on my Carrierwave Uploader. When I create a new <code>Event</code> it creates both versions correctly. But when I update it, only the file I attached gets uploaded, but versions do not get recreated.</p>
  
  <p>I am using <code>CarrierWave 1.2.2</code>, and looking at the changelog, it doesn't seem to have been a bug that got fixed in the newer versions</p>
  
  <pre class="lang-rb prettyprint-override"><code>class CoverUploader &lt; CarrierWave::Uploader::Base
    include CarrierWave::MiniMagick
  
    if Rails.env.development? || Rails.env.test?
      storage :file
    elsif Rails.env.production?
      storage :fog
    end
  
    # Override the directory where uploaded files will be stored.
    # This is a sensible default for uploaders that are meant to be mounted:
    def store_dir
      if ENV['HEROKU_APP_NAME'].to_s.include?('-pr-')
        "review_apps/#{model.class.to_s.underscore}/#{model.id}"
      else
        "#{Rails.env}/#{model.class.to_s.underscore}/#{model.id}"
      end
    end
  
    # Provide a default URL as a default if there hasn't been a file uploaded:
    def default_url(*args)
      ActionController::Base.helpers.asset_path('test.jpg')
    end
  
    # Create different versions of your uploaded files:
    version :optimised do
      process convert: 'webp'
      process :set_content_type_to_webp
  
      def full_filename(_for_file = model.cover.file)
        "cover_#{model.id}.webp"
      end
  
      def exists?
        file&amp;.exists?
      end
    end
  
    def extension_blacklist
      %w(webp)
    end
  
    private
  
    # Required to actually force Amazon S3 to treat it like an image
    def set_content_type_to_webp
      file.instance_variable_set(:@content_type, 'image/webp')
    end
  end
  </code></pre>