Fast Tokenizers save pretrained should return the list of generated file paths.
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/2918?src=pr&el=h1) Report
> Merging [#2918](https://codecov.io/gh/huggingface/transformers/pull/2918?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/2708b44ee9c151a2cdb84620d295c997af6fa7f0?src=pr&el=desc) will **increase** coverage by `0.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/2918/graphs/tree.svg?width=650&token=9qOlN6Hb1c&height=150&src=pr)](https://codecov.io/gh/huggingface/transformers/pull/2918?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #2918      +/-   ##
==========================================
+ Coverage   75.33%   75.35%   +0.01%     
==========================================
  Files          94       94              
  Lines       15444    15444              
==========================================
+ Hits        11635    11638       +3     
+ Misses       3809     3806       -3
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/2918?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/tokenization\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/2918/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy90b2tlbml6YXRpb25fdXRpbHMucHk=) | `90.58% <100%> (+0.44%)` | :arrow_up: |

------

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> Powered by [Codecov](https://codecov.io/gh/huggingface/transformers/pull/2918?src=pr&el=footer). Last update [2708b44...c10fcae](https://codecov.io/gh/huggingface/transformers/pull/2918?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
