deps: Drop support and tests for jsonschema below 4.18

Author: cwacek

setup.py

@@ -41,7 +41,7 @@
         install_requires=[
             "inflection>=0.2",
             "Markdown>=2.4",
-            "jsonschema>=2.3",
+            "jsonschema>=4.18",
             "six>=1.5.2",
         ],
         cmdclass=versioneer.get_cmdclass(),

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py{37,38,39,310,311,312}-jsonschema{23,24,25,26,30,40}-markdown{2,3}
+envlist = py{37,38,39,310,311,312}-jsonschema{40}-markdown{2,3}
 skip_missing_interpreters = true
 
 [gh-actions]
@@ -19,11 +19,6 @@ deps =
   coverage
   pytest
   pytest-mock
-  jsonschema23: jsonschema~=2.3.0
-  jsonschema24: jsonschema~=2.4.0
-  jsonschema25: jsonschema~=2.5.0
-  jsonschema26: jsonschema~=2.6.0
-  jsonschema30: jsonschema~=3.0.0
-  jsonschema40: jsonschema~=4.0
+  jsonschema40: jsonschema>=4.18
   markdown2: Markdown~=2.4
   markdown3: Markdown~=3.0