Update CHANGELOG

Summary: Update CHANGELOG to make the description more accurate

Differential Revision: D92072689

fbshipit-source-id: 48e7077fb6ed4a00705ff8ccd3c3a8f011dc92aa

Author: Jiaming You

php/CHANGELOG.md

@@ -3,7 +3,7 @@
 All notable changes to this project will be documented in this file.
 
 ## Unreleased
-- Adding support for taking request object($_SERVER in case of php) as input to the SDK.
+- Adding support for taking request context as input to the SDK.
 
 ## v1.2.1
 - Improve the is_new flag with more breakdown on net new and modified new option.