Close Reviewer menu after making selection

It looks like the Reviewer menu was made sticky (can
select multiple reviewers), however the menu was not
being closed and therefore occluding the Milestone menu.

spec/support/shared_examples/features/editable_merge_request_shared_examples.rb

@@ -15,6 +15,7 @@
     page.within '.dropdown-menu-user' do
       click_link user.name
     end
+    find('.js-reviewer-search').click
     expect(find('input[name="merge_request[reviewer_ids][]"]', visible: false).value).to match(user.id.to_s)
     page.within '.js-reviewer-search' do
       expect(page).to have_content user.name