fix huggingface/tokenizers#297 in 0.8.0
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/4882?src=pr&el=h1) Report
> Merging [#4882](https://codecov.io/gh/huggingface/transformers/pull/4882?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/02e5f79662d72cccdca81a47e3001a5f6d36e5b1&el=desc) will **increase** coverage by `0.09%`.
> The diff coverage is `0.00%`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/4882/graphs/tree.svg?width=650&height=150&src=pr&token=9qOlN6Hb1c)](https://codecov.io/gh/huggingface/transformers/pull/4882?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #4882      +/-   ##
==========================================
+ Coverage   76.46%   76.56%   +0.09%     
==========================================
  Files         128      128              
  Lines       21502    21502              
==========================================
+ Hits        16442    16462      +20     
+ Misses       5060     5040      -20     
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/4882?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/tokenization\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/4882/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy90b2tlbml6YXRpb25fdXRpbHMucHk=) | `89.69% <0.00%> (ø)` | |
| [src/transformers/modeling\_tf\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/4882/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ190Zl91dGlscy5weQ==) | `87.12% <0.00%> (-0.16%)` | :arrow_down: |
| [src/transformers/modeling\_roberta.py](https://codecov.io/gh/huggingface/transformers/pull/4882/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ19yb2JlcnRhLnB5) | `94.73% <0.00%> (+10.04%)` | :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/4882?src=pr&el=footer). Last update [02e5f79...1ce1fd3](https://codecov.io/gh/huggingface/transformers/pull/4882?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
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