chore: update changelog

CHANGELOG.md

@@ -5,10 +5,17 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 This file follows the convention described at
 [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
+## [Unreleased]
+### Added
+- npajkovsky: add negate_image() operation
+### Changed
+- npajkovsky: remove use of deprecated item `try!`, use `?` instead
+- npajkovsky: fix multiple redefined values on linux build
+
 ## [0.13.0] - 2020-03-25
 ### Added
-* danielronnkvist: Binding for MagickClutImage
-* danielronnkvist: Binding for MagickSetSize
+- danielronnkvist: Binding for MagickClutImage
+- danielronnkvist: Binding for MagickSetSize
 - max-frai: Add gaussian blur function
 
 ## [0.12.0] - 2019-09-09