Update changelog, bumping v1.0.0

Author: hollodotme

CHANGELOG.md

@@ -3,14 +3,9 @@
 All notable changes to this project will be documented in this file.
 This project adheres to [Semantic Versioning](http://semver.org/) and [Keep a CHANGELOG](http://keepachangelog.com).
 
-## [1.0.0] - YYYY-MM-DD
-
-### Added
-
-### Changed
-
-### Fixed
+## [1.0.0] - 2018-05-21
 
+First stable release.
 
 
 [1.0.0]: https://github.com/hollodotme/phpunit-testdox-markdown/tree/v1.0.0