Update CHANGELOG.md

Author: numbata

CHANGELOG.md

@@ -3,6 +3,7 @@
 #### Features
 
 * [#81](https://github.com/ruby-grape/grape-swagger-entity/pull/81): Make entity fields required by default - [@olivier-thatch](https://github.com/olivier-thatch).
+* [#85](https://github.com/ruby-grape/grape-swagger-entity/pull/85): Use rubocop plugins, use ruby 3.0 as minimum version everywhere - [@olivier-thatch](https://github.com/olivier-thatch).
 * Your contribution here.
 
 #### Fixes