fix date in CHANGELOG
@@ -8,7 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
## Unreleased
-## [v2.2.0](https://github.com/allenai/allennlp/releases/tag/v2.2.0) - 2021-04-26
+## [v2.2.0](https://github.com/allenai/allennlp/releases/tag/v2.2.0) - 2021-03-26
### Added
