[update] v9.4 release date in what's new

- release date of v9.4 set to October 22, 2026

Author: mafanya23

docs/whatsnew.md

@@ -10,7 +10,7 @@ Before updating DHTMLX to the latest version, please check the [Migration to New
 
 ## Version 9.4
 
-Released on October , 2026
+Released on October 22, 2026
 
 ### New functionality