[ios] Fixed off-by-one error due to merge

This needs to be converted into a giant switch statement, but that wouldn’t prevent issues like this cropping up in a merge anyways.

ios/app/MBXViewController.mm

@@ -262,7 +262,7 @@ static const CLLocationCoordinate2D WorldTourDestinations[] = {
     {
         [self.mapView removeAnnotations:self.mapView.annotations];
     }
-    else if (buttonIndex == actionSheet.firstOtherButtonIndex + 9)
+    else if (buttonIndex == actionSheet.firstOtherButtonIndex + 10)
     {
         [self insertCustomStyleLayer];
     }