Fixed wrong timezone while setup a different SwiftDate.defaultRegion

[cythb]

Get a wrong timezone while setup a diffent SwiftDate.defaultRegion.

    func testUTCZone() {
        SwiftDate.defaultRegion = Region(calendar: Calendars.gregorian, zone: Zones.asiaShanghai, locale: Locales.current)
        
        // DO NOT recognized the right timezone
        // The timezone should be UTC
        let wrongZone = "2020-03-13T05:40:48.000Z"
        let wrongZoneDate = Date.init(wrongZone)
        print(wrongZoneDate!.description) 
        // output: 2020-03-12 21:40:48 +0000
        // I think the correct response is : 2020-03-13 05:40:48 +0000
        XCTAssert("2020-03-13 05:40:48 +0000" == wrongZoneDate!.description)
        
        let iso8601Time = "2020-03-13T05:40:48+00:00"
        let iso8601Date = Date.init(iso8601Time)
        print(iso8601Date!.description) // output: 2020-03-13 05:40:48 +0000
        XCTAssert("2020-03-13 05:40:48 +0000" == iso8601Date!.description)
    }

[cythb]

Hi @malcommac, please take a look at this issue.