deps: Remove support for Python 3.7

+ jsonschema 4.18 doesn't support Python below 3.8, so we can't either

Author: cwacek

setup.py

@@ -47,7 +47,6 @@
         cmdclass=versioneer.get_cmdclass(),
         classifiers=[
             "Programming Language :: Python :: 3",
-            "Programming Language :: Python :: 3.7",
             "Programming Language :: Python :: 3.8",
             "Programming Language :: Python :: 3.9",
             "Programming Language :: Python :: 3.10",

tox.ini

@@ -1,10 +1,9 @@
 [tox]
-envlist = py{37,38,39,310,311,312}-jsonschema{40}-markdown{2,3}
+envlist = py{38,39,310,311,312}-jsonschema{40}-markdown{2,3}
 skip_missing_interpreters = true
 
 [gh-actions]
 python =
-  3.7: py37
   3.8: py38
   3.9: py39
   3.10: py310