Fix Elementor plugin check

Author: cssjoe

Util_Environment.php

@@ -374,6 +374,8 @@ public static function is_litespeed() {
 	 * @return bool
 	 */
 	public static function is_elementor() {
+		require_once ABSPATH . 'wp-admin/includes/plugin.php';
+
 		if ( is_plugin_active( 'Elementor\Plugin' ) ) {
 			return true;
 		} elseif ( is_plugin_active( 'elementor/elementor.php' ) ) {