BS4: Label in Horizontal mode should not be wrapped in any div element

[zraly]

According to documentation of BS4, horizontal form should not have label wrapped in a div. If does, there is additional space under every form row.

https://getbootstrap.com/docs/4.3/components/forms/#horizontal-form
https://github.com/nextras/forms-rendering/blob/master/src/Renderers/Bs4FormRenderer.php#L48