Fixed Style Inconsistency
This fixes a style inconsistency in BertForSequenceClassification's constructor where 'config' is referenced using both the parameter 'config' and 'self.config' on the same line.

This line is the only instance in modeling_bert.py where the config parameter is referenced using self.config in a constructor.
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/3976?src=pr&el=h1) Report
> Merging [#3976](https://codecov.io/gh/huggingface/transformers/pull/3976?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/4e817ff41885063e08bb3bcd63e5adfd835b9911&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `100.00%`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/3976/graphs/tree.svg?width=650&height=150&src=pr&token=9qOlN6Hb1c)](https://codecov.io/gh/huggingface/transformers/pull/3976?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #3976      +/-   ##
==========================================
- Coverage   78.44%   78.43%   -0.02%     
==========================================
  Files         111      111              
  Lines       18518    18518              
==========================================
- Hits        14527    14525       -2     
- Misses       3991     3993       +2     
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/3976?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/modeling\_bert.py](https://codecov.io/gh/huggingface/transformers/pull/3976/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ19iZXJ0LnB5) | `88.40% <100.00%> (ø)` | |
| [src/transformers/file\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/3976/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9maWxlX3V0aWxzLnB5) | `68.49% <0.00%> (-0.37%)` | :arrow_down: |
| [src/transformers/modeling\_tf\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/3976/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ190Zl91dGlscy5weQ==) | `92.59% <0.00%> (-0.17%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/huggingface/transformers/pull/3976?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/3976?src=pr&el=footer). Last update [4e817ff...6e5ef43](https://codecov.io/gh/huggingface/transformers/pull/3976?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
<|||||>Thanks @jtaylor351 !