use container as separator in flutter code example

Example: flutter reorderable list view dividers

//in children property of ReorderableListView
children: [
        for(final item in menu.dishCategories)
          Column(
            key: ValueKey(item),
            //set mainAxisSize to min to avoid items disappearing on reorder
            mainAxisSize: MainAxisSize.min,
            children: [
              ExpansionTile(
                leading: Icon(Icons.menu),
                title: Text(item, style: regularTextStyle),
                children: [

                ],
              ),
              Divider(height: 0)
            ],
          )
      ],