Update the changelog

Author: Jean85

CHANGELOG.md

@@ -5,6 +5,7 @@ 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]
+ - Add the `sentry:test` command, to test if the Sentry SDK is functioning properly.
 
 ## 3.0.0-beta2 - 2019-03-22
  - Disable Sentry's ErrorHandler, and report all errors using Symfony's events (#204)