Zero formatting behavior isn't applying to Interval formatter

[Alexandr-GlobeIn]

When you use toIntervalString / toClock methods - zero formatting behavior isn't working, because it isn't applying to func sharedFormatter() -> DateComponentsFormatter. Method don't do this:

public func apply(toFormatter formatter: DateComponentsFormatter) {
        formatter.allowsFractionalUnits = allowsFractionalUnits
	formatter.allowedUnits = allowedUnits
	formatter.collapsesLargestUnit = collapsesLargestUnit
	formatter.maximumUnitCount = maximumUnitCount
	formatter.unitsStyle = unitsStyle
	formatter.calendar = calendar
}