[update] update v9.1.1 release date

AlexKlimenkov · AlexKlimenkov · commit 065f6454c876 · 2025-12-12T16:27:45.000+03:00
diff --git a/data/whatsnew.md b/data/whatsnew.md
@@ -12,7 +12,7 @@ If your current version of dhtmlxGantt is older than 2.0, check migrating.md for
 
 9.1.1
 ---------------
-<span class='release_date'>December 12, 2025. Bugfix release</span>
+<span class='release_date'>December 15, 2025. Bugfix release</span>
 
 ### Fixes
 
