iOS 13 new UITableViewStyle

[br-zm]

RATreeView does not handle the new UITableViewStyle UITableViewStyleInsetGrouped in the method below and the default is not handled.

+ (RATreeViewStyle)treeViewStyleForTableViewStyle:(UITableViewStyle)tableViewStyle
{
  switch (tableViewStyle) {
    case UITableViewStylePlain:
      return RATreeViewStylePlain;
    case UITableViewStyleGrouped:
      return RATreeViewStyleGrouped;
  }
}

and therefore compilation fails as control may reach end of non-void function.

[mgfjx]

pod 'RATreeView', :git => 'https://github.com/mgfjxxiexiaolong/RATreeView'
可以暂时先用我修改的， 估计作者体验生活去了，没时间维护了，简单的加了default: