fix(button-group): added info about the reverted events in the changelog

Author: georgianastasov

CHANGELOG.md

@@ -2,6 +2,12 @@
 
 All notable changes for each version of this project will be documented in this file.
 
+## 15.1.33
+
+### General
+- `IgxButtonGroup`:
+    - Reverted cancellable on `selected` and `deselected` events (added in 15.1.0) as it was breaking firing order.
+
 ## 15.1.0
 
 ### New Features