Corrected "unreleased" header link

Author: shyiko

changelog.md

@@ -2,7 +2,7 @@
 All notable changes to this project will be documented in this file.  
 This project adheres to [Semantic Versioning](http://semver.org/).
 
-## [Unreleased](https://github.com/shyiko/mysql-binlog-connector-java/compare/0.2.3...HEAD)
+## [Unreleased](https://github.com/shyiko/mysql-binlog-connector-java/compare/0.2.4...HEAD)
 
 ### Added
  - Rudimentary support for GEOMETRY.