code: func (l *logger) Fatalln(vals ...interface{}) {
  	l.mut.Lock()
  	defer l.mut.Unlock()
  	s := fmt.Sprintln(vals...)
  	l.logger.Output(2, "FATAL: "+s)
  	l.callHandlers(LevelFatal, s)
  	os.Exit(1)
  }
docs: // Fatalln logs a line with a FATAL prefix and exits the process with exit
  // code 1.