Update Changelog for release of version 4.0.0

CHANGELOG.md

@@ -2,6 +2,16 @@
 
 All notable changes to the LaunchDarkly Ruby SDK will be documented in this file. This project adheres to [Semantic Versioning](http://semver.org).
 
+## [4.0.0] - 2018-05-10
+
+### Changed:
+- To reduce the network bandwidth used for analytics events, feature request events are now sent as counters rather than individual events, and user details are now sent only at intervals rather than in each event. These behaviors can be modified through the LaunchDarkly UI and with the new configuration option `inline_users_in_events`. For more details, see [Analytics Data Stream Reference](https://docs.launchdarkly.com/v2.0/docs/analytics-data-stream-reference).
+
+### Removed:
+- JRuby 1.7 is no longer supported.
+- Greatly reduced the number of indirect gem dependencies by removing `moneta`, which was previously a requirement for the Redis feature store.
+
+
 ## [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.