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!
+### Changed
+
+- Respect `preserveHtmlElements` option even when using custom PurgeCSS extractor ([#2704](https://github.com/tailwindlabs/tailwindcss/pull/2704))
 
 ## [2.0.0-alpha.5] - 2020-10-30