Update changelog

CHANGELOG.md

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 All notable changes to this project will be documented in this file. For info on how to format all future additions to this file please reference [Keep A Changelog](https://keepachangelog.com/en/1.0.0/).
 
+## [2.2.6.1] - 2022-01-17
+
+- [CVE-2022-44571] Fix ReDoS vulnerability in multipart parser
+- [CVE-2022-44570] Fix ReDoS in Rack::Utils.get_byte_ranges
+- [CVE-2022-44572] Forbid control characters in attributes (also ReDoS)
+
 ## [2.2.6] - 2022-01-17
 
 - Extend `Rack::MethodOverride` to handle `QueryParser::ParamsTooDeepError` error. ([#2011](https://github.com/rack/rack/pull/2011), [@byroot](https://github.com/byroot))