ISO8601DateFormatter prior to iOS10.swift

// This extension is only available on iOS prior to 10.0. 
// If you want to use on iOS 10.0 and later, please use ISO8601DateFormatter
extension DateFormatter {
    @available(*, obsoleted: 10.0, message: "use ISO8601DateFormatter")
    static let iso8601: DateFormatter = {
        let formatter = DateFormatter()
        formatter.calendar = Calendar(identifier: .iso8601)
        formatter.locale = Locale(identifier: "en_US_POSIX")
        formatter.timeZone = TimeZone(secondsFromGMT: 0)
        formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSXXXXX"
        return formatter
    }()
}