Update to Drupal 8.1.9. For more information, see https://www.drupal.org/project/drupal/releases/8.1.9

core/lib/Drupal/Core/Datetime/FormattedDateDiff.php

@@ -51,10 +51,23 @@ class FormattedDateDiff implements RenderableInterface, CacheableDependencyInter
   }
 
   /**
+   * {@inheritdoc}
+   */
+  public function getCacheMaxAge() {
+    return $this->maxAge;
+  }
+
+  /**
+   * The maximum age for which this object may be cached.
+   *
    * @return int
+   *   The maximum time in seconds that this object may be cached.
+   *
+   * @deprecated in Drupal 8.1.9 and will be removed before Drupal 9.0.0. Use
+   *   \Drupal\Core\Datetime\FormattedDateDiff::getCacheMaxAge() instead.
    */
   public function getMaxAge() {
-    return $this->maxAge;
+    return $this->getCacheMaxAge();
   }
 
   /**