Fix build on xcode 10.x

lib/ios/ReactNativeNavigation.m

 - (UIWindow *)initializeKeyWindow {
 	UIWindow* keyWindow = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
 	if (@available(iOS 13.0, *)) {
+#if defined(__IPHONE_OS_VERSION_MAX_ALLOWED) && __IPHONE_OS_VERSION_MAX_ALLOWED >= 130000
 		keyWindow.backgroundColor = [UIColor systemBackgroundColor];
+#endif
 	} else {
 		keyWindow.backgroundColor = [UIColor whiteColor];
 	}