Update CHANGELOG.md

Author: tom-halpin

CHANGELOG.md

@@ -5,6 +5,10 @@ All notable changes to the Sequences As Code (SaC) project will be documented in
 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).
 
+## [1.0.4] - 2020-11-16
+
+- Updated spellcheck GitHub action used
+
 ## [1.0.3] - 2020-08-24
 
 - Updated some sequence diagrams