Update changelog

Author: sebkuip

CHANGELOG.md

@@ -6,6 +6,11 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 This project mostly adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html);
 however, insignificant breaking changes do not guarantee a major version bump, see the reasoning [here](https://github.com/modmail-dev/modmail/issues/319). If you're a plugin developer, note the "BREAKING" section.
 
+# v4.1.3
+
+### Fixed
+- `use_nickname_channel_name` option would produce errors when the member was not found in the guild leading to the failure of opening modmail threads. ([PR #3368](https://github.com/modmail-dev/Modmail/pull/3368))
+
 # v4.1.2
 
 ### Fixed