Problem

If we want to run task on every 5 o'clock every day, we should set the expr like below:

batch.Cron{
	Expr: "0 5 * * *",
}

But if we set the expr to invalid format like below:

batch.Cron{
	Expr: "0 5 * * * * *",
}

It runs the task on every 5 minutes.

Expect

If the expr is invalid, error should be raised.