def files_to_check
      files = config["check"].reduce([]) { |a, e| a + Dir[e] }
      config["ignore"].reduce(files) { |a, e| a - Dir[e] }
    end
def files_to_check
      files = config["check"].reduce([]) { |a, e| a + Dir[e] }
      config["ignore"].reduce(files) { |a, e| a - Dir[e] }
    end
evaluate the files to check
 @return [Array<String>] list of files