import Error from official example caused by fastprogress
## 🐛 Bug

<!-- Important information -->

Model I am using (Bert, XLNet....): BERT

Language I am using the model on (English, Chinese....): ALL

The problem arise when using:
* [x] the official example scripts: (give details)
* [ ] my own modified scripts: (give details)

The tasks I am working on is:
* [x] an official GLUE/SQUaD task: (give the name)
* [ ] my own task or dataset: (give details)

## To Reproduce

Steps to reproduce the behavior:

V0.2.1 of fastprogress released a couple of days ago seems to cause errors in run_tf_ner.py in the official example.

Traceback (most recent call last):
  File "run_tf_ner.py", line 12, in <module>
    from fastprogress import master_bar, progress_bar
ImportError: cannot import name 'master_bar' from 'fastprogress' (/usr/local/lib/python3.7/dist-packages/fastprogress/__init__.py)

users need to either downgrade: pip3 install fastprogress==0.1.22
or change the code: 
` 
from fastprogress.fastprogress import master_bar, progress_bar
`


## Expected behavior

<!-- A clear and concise description of what you expected to happen. -->

## Environment

* OS:
* Python version:
* PyTorch version:
* PyTorch Transformers version (or branch):
* Using GPU ?
* Distributed of parallel setup ?
* Any other relevant information:

## Additional context

<!-- Add any other context about the problem here. -->

Thanks for reporting. (and hello @sgugger :)

I'll merge this to fix the immediate issue, but maybe @jplu can chime in: maybe we don't need the fastprogress dependency here?<|||||>Closed by #2400 <|||||>Oh, I forgot to update the `__init__` with the new version. Will add back the functions there to make compatibility easier. Thanks for the super quick fix!<|||||>Hello!! Thanks @julien-c for pinging me :)

Indeed my code was not compatible with the last version of fastprogress, but I thought to have specified the version in the `requirements.txt` file but apparently the way of installing the transformers framework has changed recently.

@sgugger good job, I like your fix :)

@julien-c fastprogress if (in my opinion) the most convenient progress bar to use for model training, but I can change if it becomes a problem, as you wish.
<|||||>Alright let's use `fastprogress` then! We can clean up the conditional import down the line.<|||||>I change the:
`from fastprogress import master_bar, progress_bar` 
to 
`from fastprogress.fastprogress import master_bar, progress_bar`
in the  ~/fastai/imports/core.py file and it worked