Update Changelog.md

Author: lane-formio

Changelog.md

@@ -4,6 +4,10 @@ All notable changes to this project will be documented in this file
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
+## [Unreleased: 5.12.0-rc.1]
+### Changed 
+ - Updated pdf-server@5.12.0
+
 ## 5.11.0
 ### Changed
  - Official Release