Update Changelog for release of version 5.1.0

Author: LaunchDarklyCI

CHANGELOG.md

@@ -14,6 +14,18 @@ All notable changes to the LaunchDarkly Ruby SDK will be documented in this file
 - `LDClient.all_flags()`
 
 
+## [5.1.0] - 2018-08-27
+### Added:
+- The new `LDClient` method `all_flags_state()` should be used instead of `all_flags()` if you are passing flag data to the front end for use with the JavaScript SDK. It preserves some flag metadata that the front end requires in order to send analytics events correctly. Versions 2.5.0 and above of the JavaScript SDK are able to use this metadata, but the output of `all_flags_state()` will still work with older versions.
+- The `all_flags_state()` method also allows you to select only client-side-enabled flags to pass to the front end, by using the option `client_side_only: true`.
+
+### Changed:
+- Unexpected exceptions are now logged at `ERROR` level, and exception stacktraces at `DEBUG` level. Previously, both were being logged at `WARN` level.
+
+### Deprecated:
+- `LDClient.all_flags()`
+
+
 ## [5.0.1] - 2018-07-02
 ### Fixed:
 Fixed a regression in version 5.0.0 that could prevent the client from reconnecting if the stream connection was dropped by the server.