Merge branch 'fix-mr-version-dropdowns' into 'master'

fix dropdowns for mr-versions

## What does this MR do?
Change markup of mr version dropdowns to be in line with ui guidelines so that the dropdown content is scrollable.

## Why was this MR needed?
Dropdowns were not scrolling.

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
https://gitlab.com/gitlab-org/gitlab-ce/issues/21427

cc @brycepj @dzaporozhets

See merge request !6460

app/views/projects/merge_requests/show/_versions.html.haml

@@ -10,11 +10,13 @@
             - else
               version #{version_index(@merge_request_diff)}
           %span.caret
-        %ul.dropdown-menu.dropdown-menu-selectable
+        .dropdown-menu.dropdown-select.dropdown-menu-selectable
           .dropdown-title
-            %span Version
-            %button.dropdown-title-button.dropdown-menu-close
+            %span Version:
+            %button.dropdown-title-button.dropdown-menu-close{aria: {label: "Close"}}
               = icon('times', class: 'dropdown-menu-close-icon')
+          .dropdown-content
+            %ul
               - @merge_request_diffs.each do |merge_request_diff|
                 %li
                   = link_to merge_request_version_path(@project, @merge_request, merge_request_diff), class: ('is-active' if merge_request_diff == @merge_request_diff) do
@@ -38,11 +40,13 @@
               - else
                 #{@merge_request.target_branch}
             %span.caret
-          %ul.dropdown-menu.dropdown-menu-selectable
+          .dropdown-menu.dropdown-select.dropdown-menu-selectable
             .dropdown-title
-              %span Compared with
-              %button.dropdown-title-button.dropdown-menu-close
+              %span Compared with:
+              %button.dropdown-title-button.dropdown-menu-close{aria: {label: "Close"}}
                 = icon('times', class: 'dropdown-menu-close-icon')
+            .dropdown-content
+              %ul
                 - @comparable_diffs.each do |merge_request_diff|
                   %li
                     = link_to merge_request_version_path(@project, @merge_request, @merge_request_diff, merge_request_diff.head_commit_sha), class: ('is-active' if merge_request_diff == @start_version) do