Use importlib_metadata to retrieve version

This small dependency allows us to reduce latency when importing. It can
be removed when we drop Python 3.7 support.

See also:
https://github.com/pypa/setuptools_scm/#retrieving-package-version-at-runtime

Author: kytta

setup.cfg

@@ -34,3 +34,4 @@ include_package_data = True
 python_requires = >=3.6,<4.0
 install_requires =
     Django>=2.2
+    importlib_metadata

simple_menu/__init__.py

@@ -1,9 +1,10 @@
-from pkg_resources import get_distribution, DistributionNotFound
+from importlib_metadata import PackageNotFoundError, version
+
 from .menu import Menu, MenuItem
 
 try:
-    __version__ = get_distribution("django-simple-menu").version
-except DistributionNotFound:
+    __version__ = version("django-simple-menu")
+except PackageNotFoundError:
     # package is not installed
     __version__ = None