Fix for an issue that caused WeekStartDay to fail while initializing Region

[Vignesh-Thangamariappan]

Ref: https://github.com/malcommac/SwiftDate/issues/690

[ExtremeMan]

@malcommac this seems like a valid fix for a valid bug. Can we merge it? @Vignesh-Thangamariappan can you rebase?

[ExtremeMan]

Or return back this method? https://github.com/malcommac/SwiftDate/compare/4.5.1...5.0.0#diff-4ddb0e769834923d6d637cfe9c9974c5d6d2c0e17c1703ac9ec3b7eaae5f68a9L89-L96

	/// Identify the first weekday of the calendar.
	/// By default is `sunday`.
	public var firstWeekday: WeekDay {
		set {
			self.calendar.firstWeekday = newValue.rawValue
		}
		get {
			return WeekDay(rawValue: self.calendar.firstWeekday)!
		}
	}

[Vignesh-Thangamariappan]

Sure @ExtremeMan I'm on it

[Vignesh-Thangamariappan]

@malcommac Can you please review and merge these changes. Would be helpful for people facing #690