form-control class to select box

app/views/profiles/notifications/_settings.html.haml

@@ -14,4 +14,4 @@
     = form_tag profile_notifications_path, method: :put, remote: true, class: 'update-notifications' do
       = hidden_field_tag :notification_type, type, id: dom_id(membership, 'notification_type')
       = hidden_field_tag :notification_id, membership.id, id: dom_id(membership, 'notification_id')
-      = select_tag :notification_level, options_for_select(Notification.options_with_labels, notification.level), class: 'trigger-submit'
+      = select_tag :notification_level, options_for_select(Notification.options_with_labels, notification.level), class: 'form-control trigger-submit'