Update CHANGELOG.md

Author: jarnovanleeuwen

CHANGELOG.md

@@ -6,6 +6,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+## [0.2.1] - 2018-09-27
+### Changed
+- Trace ID of requests is now included in exception messages. ([#3](https://github.com/jarnovanleeuwen/php-tikkie/pull/3))
+
 ## [0.2.0] - 2018-06-20
 ### Added
 - Added a test suite.