Right-aligned menu bar doesn't correctly stack on mobile

Created by: khawkins98

Echoing a report from @esanzgar

On mobile when there is more than one right-aligned menu option, they collide:

This is due to a margin-bottom rule that fixes a spacing issue but has unintended consequences; in https://github.com/ebiwd/EBI-Framework/blob/v1.3/css/ebi-css-build/_ebi_masthead_styles.scss#L246 :

  @media screen and (max-width: 39.9375em) {
    .masthead ul.menu.dropdown.float-right > li {
      margin-bottom: -50px;
    }
  }

Correctable by:

  @media screen and (max-width: 39.9375em) {
    .masthead ul.menu.dropdown.float-right > li:last-child {
      margin-bottom: -50px;
    }
  }