Hello, I changed the code again to support the complete 'L'

[bugfan]

Please check it when you are free
you can test like this,(or you can change your machine local time):

package main

import (
	"cron"
	"fmt"
	"time"
)

func main() {
	c := cron.New()
	c.Start()
	defer c.Stop()
	c.AddFunc("0-59 * L * 4L", func() {
		fmt.Println("test print:", time.Now())
	})
	<-(chan int)(nil)
}

[pradykaushik]

can you please resolve the build failure?

[zhufenggood]

@robfig Could you please review this PR?

[Rustin170506]

@robfig Could you please take a look?