XLM-R tokenizer is none
## Environment info

- `transformers` version: 4.3.2
- Platform: Linux-4.19.112+-x86_64-with-Ubuntu-18.04-bionic
- Python version: 3.6.9
- PyTorch version (GPU?): 1.7.0+cu101 (True)
- Tensorflow version (GPU?): 2.4.1 (True)

### Who can help
@LysandreJik @n1t0

## Information

I am using XLM-R:

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

The tasks I am working on is:
* my own task or dataset: (give details below)

## To reproduce

Steps to reproduce the behaviour:
```
tokenizer = XLMRobertaTokenizer.from_pretrained('xlm-roberta-base')
model = XLMRobertaModel.from_pretrained('xlm-roberta-base')
print(tokenizer, model)
```

## Result

The xlm-r tokenizer is none but the model can be found. 

I am a beginner for this model. Many thanks for your help.

Hello! This is weird, it shouldn't happen. Could you try to install `sentencepiece` and let me know if it fixes your issue? Thank you!<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md) are likely to be ignored.<|||||>I'm still facing this issue.

![Screenshot from 2021-05-01 16-39-09](https://user-images.githubusercontent.com/12872080/116780709-f7dc6100-aa9b-11eb-93f5-e2ab59f67035.png)
<|||||>Do you have a reproducible colab notebook? Thanks<|||||>Not sure how but it's working today.
![image](https://user-images.githubusercontent.com/12872080/116853234-5d069280-ac13-11eb-8cc9-4fa5098e27f8.png)
<|||||>This is probably because you hadn't restarted your kernel after installing the `sentencepiece` dependency!