Update CHANGELOG for v5.11 (#3128)

Signed-off-by: James Phillips <[email protected]>

Author: jamesdphillips

CHANGELOG.md

@@ -5,7 +5,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic
 Versioning](http://semver.org/spec/v2.0.0.html).
 
-## Unreleased
+## [5.11.0] - 2019-07-10
 
 ### Added
 - Silenced entries are now retrieved from the cache when determining if an event