Fixing SQL Issue: A column has been specified more than once in the order by list. Columns in the order by list must be unique.

Just had this issue on a MsSQL server. Whenever the menu items should be shown, I was facing the error from above. And I figured out, that there is indeed the `orderBy('order')` applied multiple times: Once in `Menu::display()` and the other time in the relationship itself, on `MenuItem::children`. 

Since I think it makes somehow sense to sort the MenuItems per default, I decided to remove the `orderBy` in the `Menu::display` method. But this MR is just to share the awareness of the issue, so feel free to do something else to fix the issue 😉

Have a great day! 😁