convert int to str before adding to a str
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/1487?src=pr&el=h1) Report
> Merging [#1487](https://codecov.io/gh/huggingface/transformers/pull/1487?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/6596e3d56626c921b3920e313866b7412633b91a?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/1487/graphs/tree.svg?width=650&token=9qOlN6Hb1c&height=150&src=pr)](https://codecov.io/gh/huggingface/transformers/pull/1487?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master    #1487   +/-   ##
=======================================
  Coverage   85.59%   85.59%           
=======================================
  Files          91       91           
  Lines       13526    13526           
=======================================
  Hits        11578    11578           
  Misses       1948     1948
```



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> Powered by [Codecov](https://codecov.io/gh/huggingface/transformers/pull/1487?src=pr&el=footer). Last update [6596e3d...dd904e2](https://codecov.io/gh/huggingface/transformers/pull/1487?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
<|||||>Great, thanks!