[6.x] update changelog

Author: TBlindaruk

CHANGELOG-6.x.md

@@ -1,6 +1,15 @@
 # Release Notes for 6.x
 
-## [Unreleased](https://github.com/laravel/framework/compare/v6.20.19...6.x)
+## [Unreleased](https://github.com/laravel/framework/compare/v6.20.20...6.x)
+
+
+## [v6.20.20 (2021-03-23)](https://github.com/laravel/framework/compare/v6.20.19...v6.20.20)
+
+### Added
+- Added WSREP communication link failure for lost connection detection ([#36668](https://github.com/laravel/framework/pull/36668))
+
+### Fixed
+- Fixes the issue using cache:clear with PhpRedis and a clustered Redis instance. ([#36665](https://github.com/laravel/framework/pull/36665))
 
 
 ## [v6.20.19 (2021-03-16)](https://github.com/laravel/framework/compare/v6.20.18...v6.20.19)