OSError: Model name 'facebook/bart-large-cnn' was not found in tokenizers model name list
# 🐛 Bug

## Information

Model I am using (Bart):**facebook/bart-large-cnn**

Language I am using the model on English

The problem arises when using:
* [x] the official example scripts: summarization 



## To reproduce

Steps to reproduce the behavior:    

run the code below
```python
from transformers import BartTokenizer, BartForConditionalGeneration, BartConfig
tokenizer = BartTokenizer.from_pretrained('facebook/bart-large-cnn')
```

<!-- If you have code snippets, error messages, stack traces please provide them here as well.
     Important! Use code tags to correctly format your code. See https://help.github.com/en/github/writing-on-github/creating-and-highlighting-code-blocks#syntax-highlighting
     Do not use screenshots, as they are hard to read and (more importantly) don't allow others to copy-and-paste your code.-->

## Expected behavior
load the model
<!-- A clear and concise description of what you would expect to happen. -->
## Error infomation

```
---------------------------------------------------------------------------
OSError                                   Traceback (most recent call last)
<ipython-input-5-3a96f15c5285> in <module>
----> 1 tokenizer = BartTokenizer.from_pretrained("facebook/bart-large-cnn")

~/.conda/envs/hug/lib/python3.7/site-packages/transformers/tokenization_utils_base.py in from_pretrained(cls, *inputs, **kwargs)
   1138 
   1139         """
-> 1140         return cls._from_pretrained(*inputs, **kwargs)
   1141 
   1142     @classmethod

~/.conda/envs/hug/lib/python3.7/site-packages/transformers/tokenization_utils_base.py in _from_pretrained(cls, pretrained_model_name_or_path, *init_inputs, **kwargs)
   1244                     ", ".join(s3_models),
   1245                     pretrained_model_name_or_path,
-> 1246                     list(cls.vocab_files_names.values()),
   1247                 )
   1248             )

OSError: Model name 'facebook/bart-large-cnn' was not found in tokenizers model name list (facebook/bart-base, facebook/bart-large, facebook/bart-large-mnli, facebook/bart-large-cnn, facebook/bart-large-xsum, yjernite/bart_eli5). We assumed 'facebook/bart-large-cnn' was a path, a model identifier, or url to a directory containing vocabulary files named ['vocab.json', 'merges.txt'] but couldn't find such vocabulary files at this path or url.
```

## Environment info
<!-- You can run the command `transformers-cli env` and copy-and-paste its output below.
     Don't forget to fill out the missing fields in that output! -->
     
- `transformers` version: 3.0.2
- Platform: centos
- Python version: python 3.7.0
- PyTorch version (GPU?): pytorch   1.5.0           cpu_py37hd91cbb3_0 
- Tensorflow version (GPU?): tensorflow-gpu            2.0.0
- Using GPU in script?: No
- Using distributed or parallel set-up in script?: no

Did you get this solved? I cannot load in t5-large.<|||||>> Did you get this solved? I cannot load in t5-large.

solved simply by reactivating the environment and restarting the program. I installed old version of transformers, after upgrading transformers, I forgot to deactivate the environment. 