update CHANGELOG

Author: docteurklein

src/Symfony/Bridge/Doctrine/CHANGELOG.md

@@ -9,3 +9,4 @@ CHANGELOG
  * DoctrineOrmTypeGuesser now guesses "collection" for array Doctrine type
  * DoctrineType now caches its choice lists in order to improve performance
  * DoctrineType now uses ManagerRegistry::getManagerForClass() if the option "em" is not set
+ * UniqueEntity validation constraint now accepts a "repositoryMethod" option that will be used to check for uniqueness instead of the default "findBy"