update changelog

Author: tillkruss

CHANGELOG.md

@@ -5,7 +5,7 @@ All notable changes to this project will be documented in this file.
 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]
+## [1.2.0] - 2021-05-26
 - Added Relay v0.1.0
 - Added MessagePack v2.1.2
 - Updated Swoole to v4.6.7