🐛 Fix Add Child link

The links under the Add Child dropdown was not working because the HTML
structure was not correct.  This commit will close the button tag and
then open the ul tag which allows the links to be clickable.

Ref:
  - notch8/palni_palci_knapsack#78

app/views/hyrax/base/_show_actions.html.erb

@@ -35,13 +35,14 @@
         <div class="btn-group">
           <button type="button" class="btn btn-secondary dropdown-toggle" type="button" id="dropdown-menu" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
             <%= t('.attach_child') %>
-            <ul class="dropdown-menu">
-              <% presenter.valid_child_concerns.each do |concern| %>
-                <li class="dropdown-item">
-                  <%= link_to "Attach #{concern.human_readable_type}", polymorphic_path([main_app, :new, :hyrax, :parent, concern.model_name.singular.to_sym], parent_id: presenter.id) %>
-                </li>
-              <% end %>
-            </ul>
+          </button>
+          <ul class="dropdown-menu">
+            <% presenter.valid_child_concerns.each do |concern| %>
+              <li class="dropdown-item">
+                <%= link_to "Attach #{concern.human_readable_type}", polymorphic_path([main_app, :new, :hyrax, :parent, concern.model_name.singular.to_sym], parent_id: presenter.id) %>
+              </li>
+            <% end %>
+          </ul>
         </div>
       <% end %>
       <%# OVERRIDE to validate delete permission %>