'distilbert-base-cased-distilled-squad' was not found error
# 🐛 Bug

## Information

Model I am using: distilbert-base-cased-distilled-squad

The problem arises when using: AutoTokenizer or AutoModelForQuestionAnswering

Steps to reproduce the behavior:
0. make sure you have everything on colab installed and imported 
```
!pip install transformers
import torch
from transformers import AutoModelForQuestionAnswering, AutoTokenizer
```
1. run the code on google colab:
```

tokenizer = AutoTokenizer.from_pretrained("distilbert-base-cased-distilled-squad")

model = AutoModelForQuestionAnswering.from_pretrained("distilbert-base-cased-distilled-squad")
```

and the error:
```
OSError                                   Traceback (most recent call last)
/usr/local/lib/python3.6/dist-packages/transformers/configuration_utils.py in get_config_dict(cls, pretrained_model_name_or_path, pretrained_config_archive_map, **kwargs)
    224             if resolved_config_file is None:
--> 225                 raise EnvironmentError
    226             config_dict = cls._dict_from_json_file(resolved_config_file)

OSError: 

During handling of the above exception, another exception occurred:

OSError                                   Traceback (most recent call last)
3 frames
/usr/local/lib/python3.6/dist-packages/transformers/configuration_utils.py in get_config_dict(cls, pretrained_model_name_or_path, pretrained_config_archive_map, **kwargs)
    239                     )
    240                 )
--> 241             raise EnvironmentError(msg)
    242 
    243         except json.JSONDecodeError:

OSError: Model name 'distilbert-base-cased-distilled-squad' was not found in model name list. We assumed 'https://s3.amazonaws.com/models.huggingface.co/bert/distilbert-base-cased-distilled-squad/config.json' was a path, a model identifier, or url to a configuration file named config.json or a directory containing such a file but couldn't find any such file at this path or url.
```


## Environment info     
- `transformers` version: 2.4.1
- Platform: Google Colab
- PyTorch version :1.4.0
- Using GPU in script?: no
- Using distributed or parallel set-up in script?: no

Hi! This checkpoint was added six days ago but our latest release was 13 days ago, so you would need to install the repository from source to use that model:

```
pip install git+https://github.com/huggingface/transformers
```

It'll be available in a pip install once we do a new release.