返回按钮首次标题跟随tz首选语言设置，不再跟随系统

TZImagePickerController/TZImagePickerController/TZPhotoPickerController.m

@@ -89,6 +89,8 @@ static CGFloat itemMargin = 5;
         [leftButton addTarget:self action:@selector(navLeftBarButtonClick) forControlEvents:UIControlEventTouchUpInside];
         tzImagePickerVc.navLeftBarButtonSettingBlock(leftButton);
         self.navigationItem.leftBarButtonItem = [[UIBarButtonItem alloc] initWithCustomView:leftButton];
+    } else if (tzImagePickerVc.childViewControllers.count) {
+        [tzImagePickerVc.childViewControllers firstObject].navigationItem.backBarButtonItem = [[UIBarButtonItem alloc] initWithTitle:[NSBundle tz_localizedStringForKey:@"Back"] style:UIBarButtonItemStylePlain target:nil action:nil];
     }
     _showTakePhotoBtn = _model.isCameraRoll && ((tzImagePickerVc.allowTakePicture && tzImagePickerVc.allowPickingImage) || (tzImagePickerVc.allowTakeVideo && tzImagePickerVc.allowPickingVideo));
     // [self resetCachedAssets];