require python 3.8 or greater

3.7 was my previous target, but 3.8 has been out for a while.
plus, i'm not planning on releasing this for a while,
so i can do what i want.

setup.py

@@ -6,6 +6,7 @@ setup(
     packages=[
         'respodns',
     ],
+    python_requires='>3.8.0',
 
     author='notwa',
     author_email='cloningdonor+pypi@gmail.com',
@@ -22,7 +23,7 @@ setup(
         'License :: OSI Approved :: ISC License (ISCL)',
         'Natural Language :: English',
         'Operating System :: OS Independent',
-        'Programming Language :: Python :: 3.7',
+        'Programming Language :: Python :: 3.8',
         'Programming Language :: SQL',
         'Topic :: Internet :: Name Service (DNS)',
         'Topic :: System :: Logging',