Update changelog for v1.16 (#229)

Author: nicolas-grekas

Diff for: CHANGELOG.md

@@ -1,11 +1,8 @@
 # Change Log
 
-## 1.16.0 (unreleased)
+## 1.16.0 - 2023-04-26
 
 - [#225](https://github.com/php-http/discovery/pull/225) - Remove support for the abandoned Zend Diactoros which has been replaced with Laminas Diactoros; marked the zend library as conflict in composer.json to avoid confusion
-
-## 1.15.4 - 2023-04-26
-
 - [#227](https://github.com/php-http/discovery/pull/227) - Fix handling requests with nested files
 
 ## 1.15.3 - 2023-03-31