Allow for 20.4+ line of packaging

Author: sbv-csis

setup.py

@@ -26,7 +26,7 @@
     python_requires=">=3.6",
     install_requires=[
         "deprecated>=1.2.3",
-        "packaging>=21.3",
+        "packaging>=20.4",
         'importlib-metadata >= 1.0; python_version < "3.8"',
     ],
     classifiers=[