Update changelog for 1.15.12

Author: NoahTheDuke

CHANGELOG.md

@@ -4,6 +4,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## Unreleased
+
+## 1.15.12 - 2024-05-13
+
+* Fix NPE when hashing ordered-set that contain `nil`.
+
 ## 1.15.11 - 2023-03-26
 
 * Solve native image size problem by removing runtime `resolve` [#71](https://github.com/clj-commons/ordered/issues/71)