iOS 11导航栏返回图片问题

再升级了iOS 11之后发现导航栏返回图片没有居中, 并且下方还有一条线
解决方法如下:

UIImage *backImage = [[UIImage imageNamed:@"btn_back_normal"] imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];
[[UIBarButtonItem appearance] setBackButtonTitlePositionAdjustment:UIOffsetMake(-100000, 0) forBarMetrics:UIBarMetricsDefault];
self.navigationBar.backIndicatorImage = backImage;
self.navigationBar.backIndicatorTransitionMaskImage = backImage;