chore: update changelog for release 5.1.1 with enhancements and fixes

Author: FarhanAnjum-opti

CHANGELOG.md

@@ -3,11 +3,10 @@
 ## 5.1.1
 January 20th, 2025
 
-### Bug Fixes
-* Fix Maven publish error ([#519](https://github.com/optimizely/android-sdk/pull/519)).
-
-### Enhancements
+### Enhancements and fixes
 * Upgrade Java Core SDK to 4.3.1 from 4.3.0.
+* Excludes CMAB from UserProfileService.
+* Fixes missing bucketing reasons in CMAB decision path.
 
 ## 5.1.0
 December 19th, 2025