Add #401 to CHANGELOG

Author: numbata

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 * [#400](https://github.com/ruby-grape/grape-entity/pull/400): Switch to danger-pr-comment for PR checks - [@numbata](https://github.com/numbata).
 * [#397](https://github.com/ruby-grape/grape-entity/pull/397): Reduce gem size by excluding test files - [@yuri-zubov](https://github.com/yuri-zubov).
+* [#401](https://github.com/ruby-grape/grape-entity/pull/401): Modernize gemspec: add metadata, use Dir glob, require MFA - [@numbata](https://github.com/numbata).
 * Your contribution here.
 
 #### Fixes