Update changelog entry

Author: EmilianoSanchez

CHANGES.txt

@@ -1,5 +1,5 @@
 1.15.1 (May 28, 2024)
- - Bugfixing - Restored some input validation error logs that were removed in version 1.12.0. The logs inform the user when the `getTreatment(s)` methods are called with a null or undefined value as feature flag name or flag set name.
+ - Bugfixing - Restored some input validation error logs that were removed in version 1.12.0. The logs inform the user when the `getTreatment(s)` methods are called with an invalid value as feature flag name or flag set name.
 
 1.15.0 (May 13, 2024)
  - Added an optional settings validation parameter to let overwrite the default flag spec version, used by the JS Synchronizer.