v4: justified button groups

[bellwood]

Doesn't appear to be working properly:

https://jsfiddle.net/7sqnran9/2/

Expected result is buttons stretch at equal sizes to span the entire width of its parent as per:
http://getbootstrap.com/components/#btn-groups-justified

Not sure if WIP or missing/broken

[mdo]

Dupe of #17631.

[dejurin]

<div class="btn-group d-flex" role="group">
   <a href="" class="btn btn-secondary w-100">Previous</a>
   <a href="" class="btn btn-secondary w-100">Next</a>
</div>

https://getbootstrap.com/docs/4.0/migration/#button-group

[Ohidur]

Thank you very much @dejurin