Add support for iterable datasets when val_check_interval=1.0 (Lightning-AI#1283)

* Add support for iterable datasets when val_check_interval=1.0

* Update CHANGELOG.md

Author: ethanwharris

CHANGELOG.md

@@ -22,6 +22,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Added `summary` method to Profilers. ([#1259](https://github.com/PyTorchLightning/pytorch-lightning/pull/1259))
 - Added informative errors if user defined dataloader has zero length ([#1280](https://github.com/PyTorchLightning/pytorch-lightning/pull/1280))
 - Added testing for python 3.8 ([#915](https://github.com/PyTorchLightning/pytorch-lightning/pull/915)) 
+- Added support for `IterableDataset` when `val_check_interval=1.0` (default), this will trigger validation at the end of each epoch. ([#1283](https://github.com/PyTorchLightning/pytorch-lightning/pull/1283))
 
 ### Changed