Update changelog

Author: im-denisenko

CHANGELOG.md

@@ -3,6 +3,13 @@ All notable changes to this project will be documented in this file based on the
 
 ## [Unreleased](https://github.com/ruflin/Elastica/compare/2.1.0...HEAD)
 
+### Backward Compatibility Breaks
+- Usage of constant DEBUG and method Elastica\Util::debugEnabled is removed. [#868](https://github.com/ruflin/Elastica/pull/868)
+- Elastica\Response::getTransferInfo will not return "request_header" by default. [#868](https://github.com/ruflin/Elastica/pull/868)
+
+### Bugfixes
+- Fixed segmentation fault in PHP7 [#868](https://github.com/ruflin/Elastica/pull/868)
+
 ## [2.1.0](https://github.com/ruflin/Elastica/releases/tag/2.1.0) - 2015-06-01
 
 ### Added