DeprecationWarning: distutils versions classes are deprecated.

This warning is thrown when using `oauth2==1.9.0.post1` & `Django 3.2`

```
/venv3/lib/python3.9/site-packages/oauth2/_version.py:17: DeprecationWarning: distutils Version classes are deprecated. Use packaging.version instead.
  __version__ = distutils_Version(verstr)
 ```
 
Should be easy to fix: 

```
from packaging import version
 __version__ = version(verstr)
```