Waypoint-Arrival-Screen uses incorrect API to advance index

[S2Ler]

mapbox-navigation-ios-examples/Navigation-Examples/Examples/Waypoint-Arrival-Screen.swift

Line 53 in 7fae966

navigationViewController.navigationService.routeProgress.legIndex += 1

Advance legIndex by manually changing it. It is not a proper way to change legIndex anymore. https://github.com/mapbox/mapbox-navigation-ios/blob/4d5138008b441168c9cb976d90fd84fe1c44bd10/Sources/MapboxCoreNavigation/RouteController.swift#L130 should be used instead.