log/logger.go
func (l *Logger) Errorf(format string, args ...interface{}) {
	l.Output(2, LevelError, fmt.Sprintf(format, args...))
}
func (l *Logger) Errorf(format string, args ...interface{}) {
	l.Output(2, LevelError, fmt.Sprintf(format, args...))
}
// Errorf records the log with error level