Update outdated TensorFlow -> PyTorch model transfer CLI example
The example is outdated and reports an error.
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/5296?src=pr&el=h1) Report
> Merging [#5296](https://codecov.io/gh/huggingface/transformers/pull/5296?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/7cc15bdd9675d1cec9186a8963c1f59be899ee68&el=desc) will **decrease** coverage by `0.00%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/5296/graphs/tree.svg?width=650&height=150&src=pr&token=9qOlN6Hb1c)](https://codecov.io/gh/huggingface/transformers/pull/5296?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #5296      +/-   ##
==========================================
- Coverage   79.29%   79.28%   -0.01%     
==========================================
  Files         138      138              
  Lines       24280    24280              
==========================================
- Hits        19252    19251       -1     
- Misses       5028     5029       +1     
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/5296?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/modeling\_transfo\_xl.py](https://codecov.io/gh/huggingface/transformers/pull/5296/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ190cmFuc2ZvX3hsLnB5) | `78.74% <0.00%> (-0.20%)` | :arrow_down: |
| [src/transformers/file\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/5296/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9maWxlX3V0aWxzLnB5) | `79.59% <0.00%> (ø)` | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/huggingface/transformers/pull/5296?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/huggingface/transformers/pull/5296?src=pr&el=footer). Last update [7cc15bd...65cabe0](https://codecov.io/gh/huggingface/transformers/pull/5296?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
<|||||>Could someone review this PR?<|||||>This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.
<|||||>This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.
