update changelog

Author: Johann150

codespan-reporting/CHANGELOG.md

@@ -60,6 +60,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
     ```
 
     </details>
+-   `FileId`s must now implement `Ord` instead of just `PartialEq`.
 
 ## [0.11.1] - 2021-01-18