Bump minimum Python version to 3.8

setup.py

@@ -58,17 +58,15 @@ setup(name='discord.py',
       include_package_data=True,
       install_requires=requirements,
       extras_require=extras_require,
-      python_requires='>=3.5.3',
+      python_requires='>=3.8.0',
       classifiers=[
         'Development Status :: 5 - Production/Stable',
         'License :: OSI Approved :: MIT License',
         'Intended Audience :: Developers',
         'Natural Language :: English',
         'Operating System :: OS Independent',
-        'Programming Language :: Python :: 3.5',
-        'Programming Language :: Python :: 3.6',
-        'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8',
+        'Programming Language :: Python :: 3.9',
         'Topic :: Internet',
         'Topic :: Software Development :: Libraries',
         'Topic :: Software Development :: Libraries :: Python Modules',