ImportError: cannot import name 'SAVE_STATE_WARNING' from 'torch.optim.lr_scheduler'
## Environment info
<!-- You can run the command `transformers-cli env` and copy-and-paste its output below.
     Don't forget to fill out the missing fields in that output! -->
     
- `transformers` version:
- Platform: ubuntu 18.04
- Python version: 3.7
- PyTorch version (GPU?): 1.4.0
- Tensorflow version (GPU?): 
- Using GPU in script?: no
- Using distributed or parallel set-up in script?:no

### Who can help

 Trainer: @sgugger
 



## Information

This import is not compatible with PyTorch 1.4.0 

The problem arises when using:
* [ *] the official example scripts: (give details below) 

The tasks I am working on is:
* [ *] an official GLUE/SQUaD task: (give the name) 
## To reproduce

Steps to reproduce the behavior:

```python
>>> from transformers import PreTrainedTokenizer, is_tf_available, is_torch_available
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/yuchenlin/anaconda3/envs/mcqa/lib/python3.7/site-packages/transformers/__init__.py", line 611, in <module>
    from .trainer import Trainer
  File "/home/yuchenlin/anaconda3/envs/mcqa/lib/python3.7/site-packages/transformers/trainer.py", line 69, in <module>
    from .trainer_pt_utils import (
  File "/home/yuchenlin/anaconda3/envs/mcqa/lib/python3.7/site-packages/transformers/trainer_pt_utils.py", line 26, in <module>
    from torch.optim.lr_scheduler import SAVE_STATE_WARNING
ImportError: cannot import name 'SAVE_STATE_WARNING' from 'torch.optim.lr_scheduler' (/home/yuchenlin/anaconda3/envs/mcqa/lib/python3.7/site-packages/torch/optim/lr_scheduler.py)
```
 

<!-- If you have code snippets, error messages, stack traces please provide them here as well.
     Important! Use code tags to correctly format your code. See https://help.github.com/en/github/writing-on-github/creating-and-highlighting-code-blocks#syntax-highlighting
     Do not use screenshots, as they are hard to read and (more importantly) don't allow others to copy-and-paste your code.-->

## Expected behavior

<!-- A clear and concise description of what you would expect to happen. -->

Oh I didn't check when they added this. Do you know if PyTorch 1.4.0 is the last version without it? Will add a fix this morning.<|||||>thank you for the quick fix.<|||||>`SAVE_STATE_WARNING` has been removed 3 days ago: https://github.com/pytorch/pytorch/pull/46813

Need to update https://github.com/huggingface/transformers/pull/8237 to reflect this change.