setup.py: Set Python versions to 3.7 and 3.8

Author: blazewicz

setup.py

@@ -37,14 +37,16 @@
         'Intended Audience :: System Administrators',
         'License :: OSI Approved :: MIT License',
         'Operating System :: POSIX',
-        'Programming Language :: Python :: 3 :: Only',
+        'Programming Language :: Python :: 3.7',
+        'Programming Language :: Python :: 3.8',
         'Topic :: System :: Networking',
         'Typing :: Typed',
     ],
 
     # Packages and depencies
     package_dir={'': 'src'},
     packages=find_packages('src'),
+    python_requires='~=3.7',
     install_requires=[
     ],
     extras_require={