update changelog

Author: tchaton

CHANGELOG.md

@@ -5,15 +5,7 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 
-## [1.2.3] - 2021-MM-DD
-
-### Fixed
-
-
-- Fixed DP reduction with collection ([#6324](https://github.com/PyTorchLightning/pytorch-lightning/pull/6324))
-
-
-## [1.2.2] - 2021-03-03
+## [UnReleased] - 2021-MM-DD
 
 ### Added
 
@@ -109,7 +101,8 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Fixed error thrown when using valid distributed mode in multi node ([#6297](https://github.com/PyTorchLightning/pytorch-lightning/pull/6297)
 
 
-- Added `checkpoint` parameter to callback's `on_save_checkpoint` hook ([#6072](https://github.com/PyTorchLightning/pytorch-lightning/pull/6072))
+- Fixed DP reduction with collection ([#6324](https://github.com/PyTorchLightning/pytorch-lightning/pull/6324))
+
 
 ## [1.2.1] - 2021-02-23