Change version number to "Unreleased"

Author: facelessuser

docs/changelog.md

@@ -9,7 +9,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 See the [Contributing Guide](contributing.md) for details.
 
-## [3.8.1]
+## [Unreleased]
 
 ### Fixed