Fix delegate and datasource strong refer

[131e55]

Hi! Thanks for releasing v8.0🎉

I probably found the cause of memory leak.
JTACMonthView.calendarDelegate and .calendarDataSource have strong reference.

JTACYearView has weak reference.

weak open var calendarDelegate: JTACYearViewDelegate?
weak open var calendarDataSource: JTACYearViewDataSource? {
    didSet { setupYearViewCalendar() }
}

So, I fixed JTACMonthView to have weak reference.

[patchthecode]

Thanks.
I missed that