Add packaging as dependency

Author: braniii

environment.yml

@@ -3,3 +3,4 @@ dependencies:
   - numpy
   - scipy
   - scikit-learn
+  - packaging

setup.py

@@ -21,7 +21,7 @@
 LICENSE = "new BSD"
 DOWNLOAD_URL = "https://github.com/scikit-learn-contrib/scikit-learn-extra"
 VERSION = __version__  # noqa
-INSTALL_REQUIRES = ["numpy>=1.13.3", "scipy>=0.19.1", "scikit-learn>=0.23.0"]
+INSTALL_REQUIRES = ["numpy>=1.13.3", "scipy>=0.19.1", "scikit-learn>=0.23.0", "packaging"]
 CLASSIFIERS = [
     "Intended Audience :: Science/Research",
     "Intended Audience :: Developers",