Small fix: default args for torch-lightning
Fix to the default argument passing to torch-lightning.
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/2937?src=pr&el=h1) Report
> Merging [#2937](https://codecov.io/gh/huggingface/transformers/pull/2937?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/e2a6445ebbc36121817c1f605d9a09a335f5fba5?src=pr&el=desc) will **decrease** coverage by `1.06%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/2937/graphs/tree.svg?width=650&token=9qOlN6Hb1c&height=150&src=pr)](https://codecov.io/gh/huggingface/transformers/pull/2937?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #2937      +/-   ##
==========================================
- Coverage   75.35%   74.28%   -1.07%     
==========================================
  Files          94       94              
  Lines       15445    15445              
==========================================
- Hits        11638    11473     -165     
- Misses       3807     3972     +165
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/2937?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/modeling\_tf\_pytorch\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/2937/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ190Zl9weXRvcmNoX3V0aWxzLnB5) | `8.72% <0%> (-81.21%)` | :arrow_down: |
| [src/transformers/modeling\_roberta.py](https://codecov.io/gh/huggingface/transformers/pull/2937/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ19yb2JlcnRhLnB5) | `85.91% <0%> (-9.86%)` | :arrow_down: |
| [src/transformers/modeling\_xlnet.py](https://codecov.io/gh/huggingface/transformers/pull/2937/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ194bG5ldC5weQ==) | `70.86% <0%> (-2.3%)` | :arrow_down: |
| [src/transformers/modeling\_ctrl.py](https://codecov.io/gh/huggingface/transformers/pull/2937/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ19jdHJsLnB5) | `92.07% <0%> (-2.21%)` | :arrow_down: |
| [src/transformers/modeling\_openai.py](https://codecov.io/gh/huggingface/transformers/pull/2937/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ19vcGVuYWkucHk=) | `80.2% <0%> (-1.35%)` | :arrow_down: |

------

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> Powered by [Codecov](https://codecov.io/gh/huggingface/transformers/pull/2937?src=pr&el=footer). Last update [e2a6445...34e9098](https://codecov.io/gh/huggingface/transformers/pull/2937?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
