Make group settings button white instead of gray for better visibility

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/views/layouts/nav/_group_settings.html.haml

@@ -2,7 +2,7 @@
   - if access = @group.users.find_by(id: current_user.id)
     .controls
       %span.dropdown.group-settings-dropdown
-        %a.dropdown-new.btn.btn-gray#group-settings-button{href: '#', 'data-toggle' => 'dropdown'}
+        %a.dropdown-new.btn.btn-default#group-settings-button{href: '#', 'data-toggle' => 'dropdown'}
           = icon('cog')
           = icon('caret-down')
         %ul.dropdown-menu.dropdown-menu-align-right