Added pytz to install_requires.

pytz will not automatically be installed with Django from v4.0.

Author: carltongibson

setup.py

@@ -82,7 +82,7 @@ def get_version(package):
     author_email='[email protected]',  # SEE NOTE BELOW (*)
     packages=find_packages(exclude=['tests*']),
     include_package_data=True,
-    install_requires=["django>=2.2"],
+    install_requires=["django>=2.2", "pytz"],
     python_requires=">=3.5",
     zip_safe=False,
     classifiers=[