Bug fix in checkpoint loading (Lightning-AI#1132)

Author: amoudgl

CHANGELOG.md

@@ -25,7 +25,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 ### Fixed
 
--
+- Fixed a bug to ensure lightning checkpoints to be backward compatible ([#1132](https://github.com/PyTorchLightning/pytorch-lightning/pull/1132))
 
 ## [0.7.1] - 2020-03-07