Issue #3464101 by larowlan, TomTech: revert breaking change

Closes #3464101

src/Element/Interval.php

@@ -3,14 +3,14 @@
 namespace Drupal\interval\Element;
 
 use Drupal\Core\Form\FormStateInterface;
-use Drupal\Core\Render\Element\FormElementBase;
+use Drupal\Core\Render\Element\FormElement;
 
 /**
  * Provides a form element for date/time intervals.
  *
  * @FormElement("interval")
  */
-class Interval extends FormElementBase {
+class Interval extends FormElement {
 
   /**
    * {@inheritdoc}