docs: Update changelog

Author: rekmarks

packages/eth-json-rpc-middleware/CHANGELOG.md

@@ -9,6 +9,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
+- **BREAKING:** Migrate to `JsonRpcEngineV2` ([#6976](https://github.com/MetaMask/core/pull/6976))
+  - Migrates all middleware from `JsonRpcEngine` to `JsonRpcEngineV2`.
+  - To continue using this package with the legacy `JsonRpcEngine`, use the `asLegacyMiddleware` backwards compatibility function.
 - Migrate all uses of `interface` to `type` ([#6885](https://github.com/MetaMask/core/pull/6885))
 
 ## [21.0.0]