update changelog

Author: jhunsaker

CHANGELOG.md

@@ -5,8 +5,8 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## [2.9.1] - TBD
-- [pyth] do not update twap with last price if price unknown
+## [2.9.1] - 2021-11-03
+- [pyth] do not update twap with last price if agg status is unknown
 
 ## [2.9] - 2021-11-02
 - [pyth] add minimum number of publishers for price to be valid (not unknown)