Add ability to load newer, cleaner version of Multi-News 
**Is your feature request related to a problem? Please describe.**

The [Multi-News dataloader points to the original version of the Multi-News dataset](https://github.com/huggingface/datasets/blob/12540dd75015678ec6019f258d811ee107439a73/datasets/multi_news/multi_news.py#L47), but this has [known errors in it](https://github.com/Alex-Fabbri/Multi-News/issues/11). There exists a [newer version which fixes some of these issues](https://drive.google.com/open?id=1jwBzXBVv8sfnFrlzPnSUBHEEAbpIUnFq).

Unfortunately I don't think you can just replace this old URL with the new one, otherwise this could lead to issues with reproducibility.

**Describe the solution you'd like**

Add a new version to the Multi-News dataloader that points to the updated dataset which has fixes for some known issues.

**Describe alternatives you've considered**

Replace the current URL to the original version to the dataset with the URL to the version with fixes.

**Additional context**

Would be happy to make a PR for this, could someone maybe point me to another dataloader that has multiple versions so I can see how this is handled in `datasets`?
