Update Changelog for release of version 3.0.3

Author: LaunchDarklyCI

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 All notable changes to the LaunchDarkly Ruby SDK will be documented in this file. This project adheres to [Semantic Versioning](http://semver.org).
 
+## [3.0.3] - 2018-03-23
+## Fixed
+- In the Redis feature store, fixed a synchronization problem that could cause a feature flag update to be missed if several of them happened in rapid succession.
+
 ## [3.0.2] - 2018-03-06
 ## Fixed
 - Improved efficiency of logging by not constructing messages that won't be visible at the current log level. (Thanks, [julik](https://github.com/launchdarkly/ruby-client/pull/98)!)