[pl examples] add using_native_amp flag to support pl 0.8.4
Author: amirziai
Pull request: yes

running the example `finetune_bart_tiny.sh` in `seq2seq` fails with:
```
Traceback (most recent call last):
  File "finetune.py", line 344, in <module>
    main(args)
  File "finetune.py", line 322, in main
    logger=logger,
  File "/root/notebooks/analysis/transformers/examples/lightning_base.py", line 330, in generic_train
    trainer.fit(model)
  File "/apps/python3/lib/python3.7/site-packages/pytorch_lightning/trainer/trainer.py", line 1020, in fit
    self.run_pretrain_routine(model)
  File "/apps/python3/lib/python3.7/site-packages/pytorch_lightning/trainer/trainer.py", line 1156, in run_pretrain_routine
    self.train()
  File "/apps/python3/lib/python3.7/site-packages/pytorch_lightning/trainer/training_loop.py", line 370, in train
    self.run_training_epoch()
  File "/apps/python3/lib/python3.7/site-packages/pytorch_lightning/trainer/training_loop.py", line 452, in run_training_epoch
    batch_output = self.run_training_batch(batch, batch_idx)
  File "/apps/python3/lib/python3.7/site-packages/pytorch_lightning/trainer/training_loop.py", line 659, in run_training_batch
    grad_norm_dic = self.run_batch_backward_pass(split_batch, batch_idx, opt_idx, optimizer)
  File "/apps/python3/lib/python3.7/site-packages/pytorch_lightning/trainer/training_loop.py", line 711, in run_batch_backward_pass
    self.call_optimizer_step(optimizer, opt_idx, batch_idx, split_batch)
  File "/apps/python3/lib/python3.7/site-packages/pytorch_lightning/trainer/training_loop.py", line 750, in call_optimizer_step
    using_native_amp=native_amp)
TypeError: optimizer_step() got an unexpected keyword argument 'using_native_amp'
```

seems like the issue is with the missing argument.

Comments:
What PL version are you on? The unittests should catch this.

@sshleifer `pytorch-lightning==0.8.4` which i believe is the latest

Got it.
I think you need to run `make style` to get CI to pass.
We also may need to wait to merge this until https://github.com/huggingface/transformers/pull/5361, which updates us from pl 0.8.1 to 0.8.5. (we are currently on 0.8.1, you can see in `examples/requirements.txt`).
 

# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/5556?src=pr&el=h1) Report
> Merging [#5556](https://codecov.io/gh/huggingface/transformers/pull/5556?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/9d9b872b66f9ab9b7b7c73f2c00985dd92c4121b&el=desc) will **increase** coverage by `0.36%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/5556/graphs/tree.svg?width=650&height=150&src=pr&token=9qOlN6Hb1c)](https://codecov.io/gh/huggingface/transformers/pull/5556?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #5556      +/-   ##
==========================================
+ Coverage   77.00%   77.36%   +0.36%     
==========================================
  Files         141      141              
  Lines       24638    24638              
==========================================
+ Hits        18973    19062      +89     
+ Misses       5665     5576      -89     
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/5556?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/modeling\_tf\_openai.py](https://codecov.io/gh/huggingface/transformers/pull/5556/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ190Zl9vcGVuYWkucHk=) | `20.78% <0.00%> (-74.20%)` | :arrow_down: |
| [src/transformers/tokenization\_albert.py](https://codecov.io/gh/huggingface/transformers/pull/5556/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy90b2tlbml6YXRpb25fYWxiZXJ0LnB5) | `28.84% <0.00%> (-58.66%)` | :arrow_down: |
| [src/transformers/generation\_tf\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/5556/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9nZW5lcmF0aW9uX3RmX3V0aWxzLnB5) | `82.70% <0.00%> (-3.76%)` | :arrow_down: |
| [src/transformers/modeling\_openai.py](https://codecov.io/gh/huggingface/transformers/pull/5556/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ19vcGVuYWkucHk=) | `79.72% <0.00%> (-1.38%)` | :arrow_down: |
| [src/transformers/data/processors/utils.py](https://codecov.io/gh/huggingface/transformers/pull/5556/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9kYXRhL3Byb2Nlc3NvcnMvdXRpbHMucHk=) | `27.63% <0.00%> (+1.31%)` | :arrow_up: |
| [src/transformers/tokenization\_roberta.py](https://codecov.io/gh/huggingface/transformers/pull/5556/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy90b2tlbml6YXRpb25fcm9iZXJ0YS5weQ==) | `98.63% <0.00%> (+2.73%)` | :arrow_up: |
| [src/transformers/training\_args.py](https://codecov.io/gh/huggingface/transformers/pull/5556/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy90cmFpbmluZ19hcmdzLnB5) | `77.55% <0.00%> (+11.22%)` | :arrow_up: |
| [src/transformers/data/processors/glue.py](https://codecov.io/gh/huggingface/transformers/pull/5556/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9kYXRhL3Byb2Nlc3NvcnMvZ2x1ZS5weQ==) | `49.09% <0.00%> (+17.09%)` | :arrow_up: |
| [src/transformers/trainer.py](https://codecov.io/gh/huggingface/transformers/pull/5556/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy90cmFpbmVyLnB5) | `37.96% <0.00%> (+21.29%)` | :arrow_up: |
| [src/transformers/trainer\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/5556/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy90cmFpbmVyX3V0aWxzLnB5) | `85.71% <0.00%> (+25.71%)` | :arrow_up: |
| ... and [4 more](https://codecov.io/gh/huggingface/transformers/pull/5556/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/huggingface/transformers/pull/5556?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/5556?src=pr&el=footer). Last update [9d9b872...c89d9ca](https://codecov.io/gh/huggingface/transformers/pull/5556?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).


I think this was fixed by another PR.