def current?
      output_mapping.each do |file, format|
        return false if outofdate?(file, *dnote_session.files)
      end
      "DNotes are current (#{output})"
    end
def current?
      output_mapping.each do |file, format|
        return false if outofdate?(file, *dnote_session.files)
      end
      "DNotes are current (#{output})"
    end
Check the output file and see if they are older than
 the input files.

 @return [Boolean] whether output is up-to-date