Deepset model not loading using default code
Author: gbanerjee01
Pull request: no

# 🐛 Bug

## Information

Model I am using (Bert): Bert

Language I am using the model on (English): English

The problem arises when using:
* [x] the official example scripts: (give details below)
* [ ] my own modified scripts: (give details below)

The tasks I am working on is:
* [ ] an official GLUE/SQUaD task: (give the name)
* [x] my own task or dataset: (give details below)

## To reproduce

Steps to reproduce the behavior:

1. Run this script below

```
from transformers import AutoTokenizer, AutoModelForQuestionAnswering
tokenizer = AutoTokenizer.from_pretrained("deepset/bert-large-uncased-whole-word-masking-squad2")
model = AutoModelForQuestionAnswering.from_pretrained("deepset/bert-large-uncased-whole-word-masking-squad2")
```

2. Notice this error stack:
```
---------------------------------------------------------------------------
OSError                                   Traceback (most recent call last)
<ipython-input-29-2a5e47891fb0> in <module>
----> 1 tokenizer = AutoTokenizer.from_pretrained("deepset/bert-large-uncased-whole-word-masking-squad2")
      2 model = AutoModelForQuestionAnswering.from_pretrained("deepset/bert-large-uncased-whole-word-masking-squad2")
      3 
      4 reg_tokenizer = RegexpTokenizer(r'\w+')

~/anaconda3/lib/python3.7/site-packages/transformers/tokenization_auto.py in from_pretrained(cls, pretrained_model_name_or_path, *inputs, **kwargs)
    107             return RobertaTokenizer.from_pretrained(pretrained_model_name_or_path, *inputs, **kwargs)
    108         elif 'bert' in pretrained_model_name_or_path:
--> 109             return BertTokenizer.from_pretrained(pretrained_model_name_or_path, *inputs, **kwargs)
    110         elif 'openai-gpt' in pretrained_model_name_or_path:
    111             return OpenAIGPTTokenizer.from_pretrained(pretrained_model_name_or_path, *inputs, **kwargs)

~/anaconda3/lib/python3.7/site-packages/transformers/tokenization_utils.py in from_pretrained(cls, *inputs, **kwargs)
    280 
    281         """
--> 282         return cls._from_pretrained(*inputs, **kwargs)
    283 
    284 

~/anaconda3/lib/python3.7/site-packages/transformers/tokenization_utils.py in _from_pretrained(cls, pretrained_model_name_or_path, *init_inputs, **kwargs)
    344                         pretrained_model_name_or_path, ', '.join(s3_models),
    345                         pretrained_model_name_or_path,
--> 346                         list(cls.vocab_files_names.values())))
    347 
    348         # Get files from url, cache, or disk depending on the case

OSError: Model name 'deepset/bert-large-uncased-whole-word-masking-squad2' was not found in tokenizers model name list (bert-base-uncased, bert-large-uncased, bert-base-cased, bert-large-cased, bert-base-multilingual-uncased, bert-base-multilingual-cased, bert-base-chinese, bert-base-german-cased, bert-large-uncased-whole-word-masking, bert-large-cased-whole-word-masking, bert-large-uncased-whole-word-masking-finetuned-squad, bert-large-cased-whole-word-masking-finetuned-squad, bert-base-cased-finetuned-mrpc, bert-base-german-dbmdz-cased, bert-base-german-dbmdz-uncased). We assumed 'deepset/bert-large-uncased-whole-word-masking-squad2' was a path or url to a directory containing vocabulary files named ['vocab.txt'] but couldn't find such vocabulary files at this path or url.
```

## Expected behavior

I switched to a conda environment and reinstalled transformers package with conda. Before, having used just pip install, this segment of code was working. Now, it no longer even finds the relevant model. The expected behavior is to load this specific model.

## Environment info
     
- `transformers` version: 2.11.0
- Platform: Linux-3.10.0-1062.12.1.el7.x86_64-x86_64-with-redhat-7.8-Maipo
- Python version: 3.6.8
- PyTorch version (GPU?): 1.5.1 (False)
- Tensorflow version (GPU?): not installed (NA)
- Using GPU in script?: n/a
- Using distributed or parallel set-up in script?: no


Comments:
Looks like the inference on the model hub works if it helps: https://huggingface.co/deepset/bert-large-uncased-whole-word-masking-squad2?text=Where+do+I+live%3F&context=My+name+is+Wolfgang+and+I+live+in+Berlin