log/logger.go
func (l *Logger) Warnln(args ...interface{}) {
	l.Output(2, LevelWarn, fmt.Sprintln(args...))
}
func (l *Logger) Warnln(args ...interface{}) {
	l.Output(2, LevelWarn, fmt.Sprintln(args...))
}
// Warnln records the log with warn level