Update CHANGELOG for release

Author: trsmith2

CHANGELOG.md

@@ -1,7 +1,7 @@
 # Change Log
 All notable changes to this project will be documented in this file.
 
-## [Unreleased]
+## [0.2.1] 2016-12-12
 ### Changed
 - Externalized build logic from Jenkins to shell script so it can be reused
 - Refactored the information returned by the Application Detail API to include the YARN application state and also to return information for jobs that have ended. Made the implementation more performant by using the YARN Resource Manager REST API instead of the CLI.