Update changelog

Author: yatsukhnenko

Changelog.md

@@ -7,6 +7,10 @@ and PhpRedis adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 ## [Unreleased]
 
+---
+
+## [5.1.1] - 2019-11-11 ([GitHub](https://github.com/phpredis/phpredis/releases/tag/5.1.1), [PECL](https://pecl.php.net/package/redis/5.1.1))
+
 ### Fixed
 
 - Fix fail to connect to redis through unix socket