update changelog

Author: RobinMalfait

CHANGELOG.md

@@ -40,6 +40,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Don't emit generated utilities with invalid uses of theme functions ([#9319](https://github.com/tailwindlabs/tailwindcss/pull/9319))
 - Revert change that only listened for stdin close on TTYs ([#9331](https://github.com/tailwindlabs/tailwindcss/pull/9331))
 - Ignore unset values (like `null` or `undefined`) when resolving the classList for intellisense ([#9385](https://github.com/tailwindlabs/tailwindcss/pull/9385))
+- Implement fallback plugins when arbitrary values result in css from multiple plugins ([#9376](https://github.com/tailwindlabs/tailwindcss/pull/9376))
 
 ## [3.1.8] - 2022-08-05