Summarization Examples: add Bart CNN Evaluation
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/3082?src=pr&el=h1) Report
> Merging [#3082](https://codecov.io/gh/huggingface/transformers/pull/3082?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/b74c9b106b97b0722ff8f98e77e2e2210c688b23?src=pr&el=desc) will **increase** coverage by `0.4%`.
> The diff coverage is `87.27%`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/3082/graphs/tree.svg?width=650&token=9qOlN6Hb1c&height=150&src=pr)](https://codecov.io/gh/huggingface/transformers/pull/3082?src=pr&el=tree)

```diff
@@           Coverage Diff            @@
##           master   #3082     +/-   ##
========================================
+ Coverage   77.19%   77.6%   +0.4%     
========================================
  Files          98      98             
  Lines       16063   16219    +156     
========================================
+ Hits        12400   12586    +186     
+ Misses       3663    3633     -30
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/3082?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/tokenization\_bart.py](https://codecov.io/gh/huggingface/transformers/pull/3082/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy90b2tlbml6YXRpb25fYmFydC5weQ==) | `100% <100%> (ø)` | :arrow_up: |
| [src/transformers/configuration\_bart.py](https://codecov.io/gh/huggingface/transformers/pull/3082/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9jb25maWd1cmF0aW9uX2JhcnQucHk=) | `100% <100%> (ø)` | :arrow_up: |
| [src/transformers/modeling\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/3082/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ191dGlscy5weQ==) | `92.76% <76.66%> (+0.38%)` | :arrow_up: |
| [src/transformers/modeling\_bart.py](https://codecov.io/gh/huggingface/transformers/pull/3082/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ19iYXJ0LnB5) | `93.05% <88.82%> (+8.47%)` | :arrow_up: |

------

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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/huggingface/transformers/pull/3082?src=pr&el=footer). Last update [b74c9b1...5656b5e](https://codecov.io/gh/huggingface/transformers/pull/3082?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
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New organization @LysandreJik <|||||>I like that organisation