Update CHANGELOG.md

Author: reinink

CHANGELOG.md

@@ -7,7 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
-- Nothing yet!
+### Fixed
+
+- Reduce specificity of `abbr` rule in preflight ([#6671](https://github.com/tailwindlabs/tailwindcss/pull/6671))
 
 ## [3.0.7] - 2021-12-17