Deberta Tokenizatiion
## Environment info

- `transformers` version: 4.0.0
- Platform: Linux
- Python version: 3.8
- PyTorch version (GPU?): 1.7

### Who can help
@BigBird01 @LysandreJik 

## Information

I'd like to use the new deberta model, but it seems that the tokens aren't mapped correctly?

```
from transformers import AutoTokenizer

test_string = 'hello, I am a dog'

tokenizer = AutoTokenizer.from_pretrained('roberta-base')
print('Roberta output is: ', tokenizer.tokenize(test_string))

tokenizer = AutoTokenizer.from_pretrained('microsoft/deberta-base')
print('Deberta output is: ', tokenizer.tokenize(test_string))
```

Roberta output is:  ['hello', ',', 'ĠI', 'Ġam', 'Ġa', 'Ġdog']
Deberta output is:  ['31373', '11', '314', '716', '257', '3290']

I'd expect deberta to give an output similar to roberta, rather than numbers.
@LysandreJik any update on this?<|||||>@yaysummeriscoming  To get sub words instead of numbers, you can call `tokenizer.gpt2_tokenizer.decode(tokens)`. Please take a look at [our code](https://github.com/huggingface/transformers/blob/52c9e842854a701a7d1b608600a614278b4407d3/src/transformers/tokenization_deberta.py#L396) for reference.<|||||>That did the trick, thanks!