Numpy compatibility for sentence piece
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/2191?src=pr&el=h1) Report
> Merging [#2191](https://codecov.io/gh/huggingface/transformers/pull/2191?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/ceae85ad60da38cacb14eca49f752669a4fe31dc?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/2191/graphs/tree.svg?width=650&token=9qOlN6Hb1c&height=150&src=pr)](https://codecov.io/gh/huggingface/transformers/pull/2191?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #2191      +/-   ##
==========================================
- Coverage   79.92%   79.92%   -0.01%     
==========================================
  Files         131      131              
  Lines       19469    19470       +1     
==========================================
  Hits        15561    15561              
- Misses       3908     3909       +1
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/2191?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [transformers/tokenization\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/2191/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL3Rva2VuaXphdGlvbl91dGlscy5weQ==) | `92.1% <100%> (+0.01%)` | :arrow_up: |
| [transformers/tests/utils.py](https://codecov.io/gh/huggingface/transformers/pull/2191/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL3Rlc3RzL3V0aWxzLnB5) | `90.62% <0%> (-3.13%)` | :arrow_down: |

------

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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/huggingface/transformers/pull/2191?src=pr&el=footer). Last update [ceae85a...cb6d54b](https://codecov.io/gh/huggingface/transformers/pull/2191?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
<|||||>Awesome!