Update changelog

Author: adamwathan

CHANGELOG.md

@@ -7,7 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
-- Nothing yet!
+### Added
+
+- Support flattening deeply nested color objects ([#2148](https://github.com/tailwindlabs/tailwindcss/pull/2148))
 
 ## [2.0.0-alpha.2] - 2020-10-25