Adds CHANGELOG entry for #272

Author: michalbundyra

CHANGELOG.md

@@ -22,7 +22,9 @@ All notable changes to this project will be documented in this file, in reverse
 
 ### Fixed
 
-- Nothing.
+- [#272](https://github.com/zendframework/zend-validator/pull/272) changes
+  curly braces in array and string offset access to square brackets
+  in order to prevent issues under the upcoming PHP 7.4 release.
 
 ## 2.12.0 - 2019-01-30