[Bug][TreeList] The dynamically added header class is not available in the DOM

[vveesseelliinnaa]

The dynamically added CSS class to the headerClassName is not updated in the DOM. If the class is configured directly in the component props, its is applied successfully.

To Reproduce Steps to reproduce the behavior:

1.Got to https://codesandbox.io/s/affectionate-cloud-jy67sv?file=/src/main.vue:2569-2583 2. Click one of the column menus and sort a column

Expected behavior The active class is added to the column header element like in the following Grid sample (the filter button is styled based on it): https://www.telerik.com/kendo-vue-ui/components/grid/columns/column-menu/

Video http://somup.com/c06hXeBZC0