chore: clarify changelog

Author: mfn

CHANGELOG.md

@@ -5,7 +5,8 @@ CHANGELOG
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 ### Fixed
-- Middleware and methods can be used in class based schemas. [\#724 / jasonvarga](https://github.com/rebing/graphql-laravel/pull/724)
+- Middleware and methods can be used in class based schemas. [\#724 / jasonvarga](https://github.com/rebing/graphql-laravel/pull/724)\
+  This is a follow-up fix for [Support for class based schemas](https://github.com/rebing/graphql-laravel/pull/706)
 
 2021-03-31, 6.4.0
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