[ios] set attributed text to nav title

nav_title_attrs.m

    NSShadow *shadow = [[NSShadow alloc] init];
    [shadow setShadowOffset:CGSizeMake(1, 1)];
    [shadow setShadowColor:[UIColor blackColor]];
    [shadow setShadowBlurRadius:1];
    navigationController.navigationBar.titleTextAttributes = @{NSForegroundColorAttributeName: [UIColor whiteColor], NSShadowAttributeName: shadow};