cannot import name 'DataCollatorForSeq2Seq' from 'transformers'
## Environment info

- `transformers` version:  4.13.0.dev0
- Platform: Ubuntu
- Python version: 3.7
- PyTorch version (GPU?): 1.10.0


### Who can help
@sgugger

## Models:
- encoder-decoder models


## To reproduce

Steps to reproduce the behavior:
`git clone https://github.com/huggingface/transformers.git`
`cd transformers`
`pip install -e .`

![image](https://user-images.githubusercontent.com/56379157/143610360-fc75a023-6a03-4cc2-9532-2fc4a684e5a7.png)
![image](https://user-images.githubusercontent.com/56379157/143610551-03701cde-8527-4df8-a7cb-e4541eb59aa4.png)
The class  DataCollatorForSeq2Seq  is  in  data_collator.py.   I don't know why this error occurs.   Could you help me to solve it?



After restarting jupyter, the problem is solved.