Dependency version check fails for tokenizers
## Environment info

- `transformers` version: 4.5.0
- Platform: Linux-4.15.0-134-generic-x86_64-with-glibc2.10
- Python version: 3.8.5
- PyTorch version (GPU?): 1.8.1 (False)
- Tensorflow version (GPU?): 2.4.0 (False)
- Using GPU in script?: N/A
- Using distributed or parallel set-up in script?: N/A
- `tokenizers` version: 0.10.2 (checked also 0.10.1)

### Who can help
@stas00, @sgugger
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Library:

- benchmarks: @patrickvonplaten
- deepspeed: @stas00
- ray/raytune: @richardliaw, @amogkam
- text generation: @patrickvonplaten
- tokenizers: @LysandreJik
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## Information

When importing `transformers`, the new dependency version check code (#11061) seems to fail for the tokenizers library:
`importlib.metadata.version('tokenizers')` returns None instead of the version string.


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

## To reproduce

Steps to reproduce the behavior:

1. `import transformers`

```
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/guyrosin/miniconda3/envs/pt/lib/python3.8/site-packages/transformers/__init__.py", line 43, in <module>
    from . import dependency_versions_check
  File "/home/guyrosin/miniconda3/envs/pt/lib/python3.8/site-packages/transformers/dependency_versions_check.py", line 41, in <module>
    require_version_core(deps[pkg])
  File "/home/guyrosin/miniconda3/envs/pt/lib/python3.8/site-packages/transformers/utils/versions.py", line 101, in require_version_core
    return require_version(requirement, hint)
  File "/home/guyrosin/miniconda3/envs/pt/lib/python3.8/site-packages/transformers/utils/versions.py", line 92, in require_version
    if want_ver is not None and not ops[op](version.parse(got_ver), version.parse(want_ver)):
  File "/home/guyrosin/miniconda3/envs/pt/lib/python3.8/site-packages/packaging/version.py", line 57, in parse
    return Version(version)
  File "/home/guyrosin/miniconda3/envs/pt/lib/python3.8/site-packages/packaging/version.py", line 296, in __init__
    match = self._regex.search(version)
TypeError: expected string or bytes-like object
```

The root problem is this:
```python
from importlib.metadata import version
version('tokenizers') # returns None
```


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## Expected behavior

<!-- A clear and concise description of what you would expect to happen. -->
`importlib.metadata.version('tokenizers')` should return its version string.
Thank you for this report, @guyrosin 

Any idea how we could reproduce this problem? This works for me:
```
$ python -c "from importlib.metadata import version; print(version('tokenizers'))"
0.10.1
```

I do see a different problem though. I see we now have: `"tokenizers>=0.10.1,<0.11"`

I didn't expect a range definition, when I wrote this code, so currently it tries to do:
```
version.parse('0.10.0') > version.parse('0.10.1,<0.11')
```
which is wrong - I'm surprised `version.parse` doesn't assert, it just quietly returns the same unparsed string `0.10.1,<0.11`
so this definitely needs to be fixed to split by ',' and test each condition separately.

Actually does the problem go away if you edit `transformers/dependency_versions_table.py` to use just `"tokenizers>=0.10.1"`?

Also if you could add a debug print and see what's in `got_ver` and `want_ver` just before it fails to `version.parse`. I think this is the real culprit according to the trace. i.e. it's not that it can't find `tokenizers` - but it fails to parse one of the 2 version inputs.

Thanks.<|||||>Could you please give a try to this PR: https://github.com/huggingface/transformers/pull/11110 and let me know if the problem goes away? Thank you.
<|||||>Thanks for the fast response @stas00! I'm glad this helped you find another bug :)

I guess the problem in my case is with the tokenizers distribution. I'm getting:
```
$ python -c "from importlib.metadata import version; print(version('tokenizers'))"
None
```
Even after reinstalling `tokenizers`.
So trying your PR results in "got_ver is None" (`want_ver` is 0.10.1)
No idea how to reproduce it though :\

Edit: to make it clear: using `pkg_resources` instead of `importlib` works:
```
$ python -c "import pkg_resources; print(pkg_resources.get_distribution('tokenizers').version)"
0.10.1
```<|||||>Does it help if you update/explicitly install this library:
```
pip install importlib_metadata -U
```
and then retry?

It's good to know that `pkg_resources` does report the right thing. But it also has a cache which apparently reports the past state and not the current, which is the main reason it was replaced.

But sometimes the `site-packages` folder gets messed up. 

Does it make any difference if you first uninstall `tokenizers` **twice** in a row and then install it (I know you said you reinstalled it, but this is slightly different)

What if you create a new environment and try there?<|||||>OK, it seems like my environment was corrupted indeed - there was a `tokenizers-0.9.4.dist-info` folder inside my env's `site-packages` folder... After deleting it (manually) and reinstalling `tokenizers`, everything works!
Thanks a lot for your help @stas00!<|||||>Yay! Glad it worked, @guyrosin!