Update changelog

Author: ksassnowski

CHANGELOG.md

@@ -5,6 +5,13 @@ 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/), 
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.4.0] — 2021-07-20
+
+### Changed
+
+- Bump Arcanist dependency to `^0.4.0`
+- Change return type declarations to match `ResponseRenderer` interface
+
 ## [0.3.0] — 2021-06-29
 
 ### Changed