Set changelog to 1.2.1

Author: todi1856

com.unity.mobile.android-logcat/CHANGELOG.md

@@ -4,7 +4,7 @@ All notable changes to this package will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
-## [Unreleased] - 2021-01-01
+## [1.2.1] - 2021-01-21
 
 ### Fix & Improvements.
  - Removed limitation where Android Logcat could only be used while the active Editor platform is Android. Note: Android Support is still required to be installed for Android Logcat to work.