Dropping support for python 3.7 (#505)

* dropped support for 3.7

* added python 3.9 and 3.10 to classifiers

Author: levmckinney

setup.py

@@ -95,7 +95,7 @@ def run(self):
     long_description=get_readme(),
     long_description_content_type="text/markdown",
     author="Center for Human-Compatible AI and Google",
-    python_requires=">=3.7.0",
+    python_requires=">=3.8.0",
     packages=find_packages("src"),
     package_dir={"": "src"},
     package_data={"imitation": ["py.typed", "envs/examples/airl_envs/assets/*.xml"]},
@@ -161,8 +161,9 @@ def run(self):
         "License :: OSI Approved :: MIT License",
         "Programming Language :: Python",
         "Programming Language :: Python :: 3",
-        "Programming Language :: Python :: 3.7",
         "Programming Language :: Python :: 3.8",
+        "Programming Language :: Python :: 3.9",
+        "Programming Language :: Python :: 3.10",
         "Programming Language :: Python :: Implementation :: CPython",
         "Programming Language :: Python :: Implementation :: PyPy",
     ],