Update modeling_utils.py by adding "DUMMY_INPUTS" after "logger" variable.
This Pull Request fixes a probable bug found using Transformers in Anaconda, using TFBertForSequenceClassification, Tensorflow 2.0.0b0, according to:

https://github.com/huggingface/transformers/issues/1810#issuecomment-554572471


# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/1847?src=pr&el=h1) Report
> Merging [#1847](https://codecov.io/gh/huggingface/transformers/pull/1847?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/0477b307c7501ea76e01b03cb387a2312db752b3?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/1847/graphs/tree.svg?width=650&token=9qOlN6Hb1c&height=150&src=pr)](https://codecov.io/gh/huggingface/transformers/pull/1847?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #1847      +/-   ##
==========================================
+ Coverage   84.08%   84.08%   +<.01%     
==========================================
  Files          97       97              
  Lines       14316    14317       +1     
==========================================
+ Hits        12037    12038       +1     
  Misses       2279     2279
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/1847?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [transformers/modeling\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/1847/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL21vZGVsaW5nX3V0aWxzLnB5) | `89.67% <100%> (+0.02%)` | :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/1847?src=pr&el=footer). Last update [0477b30...07bda77](https://codecov.io/gh/huggingface/transformers/pull/1847?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
<|||||>I think this bug is already fixed on master.<|||||>It should be fixed the latest release (2.2.1).
Feel free to reopen if it's not the case.