[Docs] Role "button" in Navbar dropdowns

Created by: AlessandroVecchi

hi, in the first example https://getbootstrap.com/docs/4.1/components/navbar/#supported-content .dropdown-toggle has a "role="button" in the second example https://getbootstrap.com/docs/4.1/components/navbar/#nav "role=button" is missing

which is the correct version?