More code cleanup

inc/list-tables/class-membership-list-table-widget.php

@@ -277,5 +277,5 @@ class Membership_List_Table_Widget extends Base_List_Table {
 	 * @since 2.0.0
 	 * @return void
 	 */
-	public function _js_vars() {}
+	public function _js_vars(): void {}
 }

inc/list-tables/class-payment-list-table-widget.php

@@ -241,5 +241,5 @@ class Payment_List_Table_Widget extends Base_List_Table {
 	 * @since 2.0.0
 	 * @return void
 	 */
-	public function _js_vars() {}
+	public function _js_vars(): void {}
 }