Fixing the changelog semantics

Signed-off-by: Fabio José <[email protected]>

Author: fabiojose

CHANGELOG.md

@@ -5,7 +5,9 @@ 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/)
 
 ## [Unreleased]
-### Changed
+
+## [0.3.1]
+### Fixed
 - Axios version to `0.18.1` due the CVE-2019-10742
 - Fix the `subject` attribute unmarshal error: issue
 [#32](https://github.com/cloudevents/sdk-javascript/issues/32)