Update version number in changelog [ci skip]
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5299801..f8a2ce3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,7 +4,7 @@
 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]
+## [0.4.0-pre.0] - 2017-12-11
 ### Added
 - `JitterRng` added as a high-quality alternative entropy source using the
   system timer