Update CHANGELOG for v2.1.3

Author: paulbalandan

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this library 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).
 
+## [v2.1.3](https://github.com/NexusPHP/cs-config/compare/v2.1.2..v2.1.3) - 2021-01-07
+
+### Fixed
+
+- Fixed a PHPStan error on the incorrect covariant return type of `Factory::invoke`.
+
 ## [v2.1.2](https://github.com/NexusPHP/cs-config/compare/v2.1.1..v2.1.2) - 2021-01-07
 
 ### Fixed