previous method
Returns the previous instance of the given date considering this Every
base process.
If the date is a DateTime that matches the Every pattern, a new
DateTime will be generated.
Implementation
@override
DateTime previous(DateTime date) {
if (date.day > dueDay) {
return _monthsDay(date, monthDelta: 0);
} else {
return _monthsDay(date, monthDelta: -1);
}
}