def downloaded_file
      filename = source[:cached_name] if source[:cached_name]
      filename ||= File.basename(source[:url], "?*")
      File.join(Config.cache_dir, filename)
    end
def downloaded_file
      filename = source[:cached_name] if source[:cached_name]
      filename ||= File.basename(source[:url], "?*")
      File.join(Config.cache_dir, filename)
    end
The path on disk to the downloaded asset. The filename is defined by
 +source :cached_name+. If ommited, then it comes from the software's
 +source :url+ value

 @return [String]