update changelog to stable version

Author: rhpvorderman

CHANGELOG.md

@@ -8,7 +8,7 @@ Newest changes should be on top.
 This document is user facing. Please word the changes in such a way
 that users understand how the changes affect the new version.
 -->
-version 1.4.0-dev
+version 1.4.0
 -----------------
 + Update versions of Fastqc and Cutadapt.