#19 update version

Author: rez1dent3

changelog.md

@@ -5,6 +5,8 @@ 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).
 
 ## [Unreleased]
+
+## [2.2.0] - 2018-12-25
 ### Added 
 - Add trait `CanPay`.
 - Add trait `CanPayFloat`.