Fix #684

[Caellion]

Fixes #684

Attempts to fix using @nielsuit227's code

Note: This creates a dependency on importlib-metadata for Python 3.7

Also note: I am not sure how to update setup to conditionally depend on importlib-metadata, please advise

[Andrew-Chen-Wang]

If possible, to avoid the dependency, can you use the old code when Python < 3.8 in your if else statement? Thank you

[Caellion]

If possible, to avoid the dependency, can you use the old code when Python < 3.8 in your if else statement? Thank you

On python 3.7.11 it breaks with NameError: name 'DistributionNotFound' is not defined

I think I will have to keep dependency on importlib-metadata on python 3.7

[aqeelat]

why not hardcode the version in __init__.py and then change setup.py to read the version from it?

[grizmio]

what do you think about something like this ugly example:

import sys

if sys.version_info >= (3, 8):
    from importlib import metadata
    try:
        __version__ = metadata.version("djangorestframework_simplejwt")
    except metadata.PackageNotFoundError:
        # package is not installed
        __version__ = None
else:
    from pkg_resources import DistributionNotFound, get_distribution

    try:
        __version__ = get_distribution("djangorestframework_simplejwt").version
    except DistributionNotFound:
        # package is not installed
        __version__ = None