Show divider line under tabs in mobile layout

ee/app/views/shared/issuable/_epic_nav.html.haml

@@ -2,7 +2,7 @@
 - page_context_word = type.to_s.humanize(capitalize: false)
 - display_count = local_assigns.fetch(:display_count, :true)
 
-%ul.nav-links.epics-state-filters
+%ul.nav-links.mobile-separator.epics-state-filters
   %li{ class: active_when(params[:state] == 'opened') }>
     = link_to page_filter_path(state: 'opened', label: true), id: 'state-opened', title: (_("Filter by %{issuable_type} that are currently opened.") % { issuable_type: page_context_word }), data: { state: 'opened' } do
       #{issuables_state_counter_text(type, :opened, display_count)}