fixed typo in Changelog [ci skip]

Author: vimishor

CHANGELOG.md

@@ -4,7 +4,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased]
 
-## Fixed:
+### Fixed:
   - Declining a PR without a `message` parameter caused a 500 response. (issue #43)