Update to Drupal 8.2.0. For more information, see https://www.drupal.org/project/drupal/releases/8.2.0

core/lib/Drupal/Core/GeneratedLink.php

@@ -14,6 +14,11 @@ use Drupal\Core\Render\BubbleableMetadata;
  */
 class GeneratedLink extends BubbleableMetadata implements MarkupInterface, \Countable {
 
+  /**
+   * HTML tag to use when building the link.
+   */
+  const TAG = 'a';
+
   /**
    * The HTML string value containing a link.
    *