fixes #8968
**This is the same PR as: [link](https://github.com/huggingface/transformers/pull/8991#issue-534604029). I was asked to create a new one due to a merge mistake.**

# What does this PR do? (Text of the previous PR)

One of the 3.X releases introduced output objects that replaced the previously returned tuples. This PR updates the transformers notebook to reflect that update.


Fixes #8968


## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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      Pull Request section?
- [x] Was this discussed/approved via a Github issue or the [forum](https://discuss.huggingface.co/)? Please add a link
      to it if that's the case.
- [ ] Did you make sure to update the documentation with your changes? Here are the
      [documentation guidelines](https://github.com/huggingface/transformers/tree/master/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/master/docs#writing-source-documentation).
- [ ] Did you write any new necessary tests?


## Who can review?

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@patrickvonplaten
@LysandreJik