Update Changelog for release of version 3.5.2

Author: LaunchDarklyCI

CHANGELOG.md

@@ -2,6 +2,11 @@
 
 All notable changes to the LaunchDarkly PHP SDK will be documented in this file. This project adheres to [Semantic Versioning](http://semver.org).
 
+## [3.5.2] - 2019-04-11
+### Fixed:
+- In the 3.5.1 release, the `VERSION` constant was incorrectly still reporting the version as "3.5.0". The constant is now correct. There are no other changes in this release.
+
+
 ## [3.5.1] - 2019-04-03
 ### Fixed:
 - Setting user attributes to non-string values when a string was expected would cause analytics events not to be processed. The SDK will now convert attribute values to strings as needed.