Update CHANGELOG

Author: Ciarán O'Mara

CHANGELOG.md

@@ -7,6 +7,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [0.4.1]
+
+### Added
+- Added flag tests.
+
+### Fixed
+- Corrected `isproperpair` method ([#67](https://github.com/BioJulia/XAM.jl/pull/67)).
 
 ## [0.4.0]