Update CHANGELOG.md

Author: justusschock

CHANGELOG.md

@@ -162,6 +162,8 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 ### Fixed
 
+- Fixed `apply_to_collection` works on Custom Collections now ([#7851](https://github.com/PyTorchLightning/pytorch-lightning/pull/7851))
+
 - Fixed ambiguous warning when both overfit and train dataloader shuffling are enabled ([#7685](https://github.com/PyTorchLightning/pytorch-lightning/pull/7685))
 
 - Fixed dataloaders are not reset when tuning the model ([#7566](https://github.com/PyTorchLightning/pytorch-lightning/pull/7566))