code: function format (str, tokens) {
    for (let i = 0; i < tokens.length; i++) {
      str = str.replace(tokens[i].token, tokens[i].replacement)
    }
    return str
  }
docs: Return formatted log line.
  
  @param  {String} str
  @param  {IncomingMessage} req
  @param  {ServerResponse} res
  @return {String}
  @api private