Remove hacks from ScheduledJobs cron spec parsing

Previusly github.com/robfig/cron library did not allow passing cron spec without
seconds. Previous commit updates the library, which has additional
method ParseStandard which follows the standard cron spec, iow. minute,
hour, day of month, month, day of week.

pkg/apis/batch/validation/validation.go

@@ -199,12 +199,7 @@ func validateConcurrencyPolicy(concurrencyPolicy *batch.ConcurrencyPolicy, fldPa
 
 func validateScheduleFormat(schedule string, fldPath *field.Path) field.ErrorList {
 	allErrs := field.ErrorList{}
-	// TODO soltysh: this should be removed when https://github.com/robfig/cron/issues/58 is fixed
-	tmpSchedule := schedule
-	if len(schedule) > 0 && schedule[0] != '@' {
-		tmpSchedule = "0 " + schedule
-	}
-	if _, err := cron.Parse(tmpSchedule); err != nil {
+	if _, err := cron.ParseStandard(schedule); err != nil {
 		allErrs = append(allErrs, field.Invalid(fldPath, schedule, err.Error()))
 	}