[6.x] update changelog

Author: TBlindaruk

CHANGELOG-6.x.md

@@ -1,6 +1,16 @@
 # Release Notes for 6.x
 
-## [Unreleased](https://github.com/laravel/framework/compare/v6.20.20...6.x)
+## [Unreleased](https://github.com/laravel/framework/compare/v6.20.21...6.x)
+
+
+## [v6.20.21 (2021-03-30)](https://github.com/laravel/framework/compare/v6.20.20...v6.20.21)
+
+### Added
+- Added support of DynamoDB in CI suite ([#36749](https://github.com/laravel/framework/pull/36749))
+- Support username parameter for predis ([#36762](https://github.com/laravel/framework/pull/36762))
+
+### Changed
+- Use qualified column names in pivot query ([#36720](https://github.com/laravel/framework/pull/36720))
 
 
 ## [v6.20.20 (2021-03-23)](https://github.com/laravel/framework/compare/v6.20.19...v6.20.20)