Allow jsonschema >4.0.0 (#55)

Version 4.0.0 of jsonschema was released on Sep 30, 2021. It's really
hard to use this lib when it is locking down to old dependencies and
never updating them.

setup.cfg

@@ -19,7 +19,7 @@ package_dir =
 # DON'T CHANGE THE FOLLOWING LINE! IT WILL BE UPDATED BY PYSCAFFOLD!
 install_requires =
     importlib-metadata; python_version<"3.8"
-    jsonschema >= 3.0.0,<4
+    jsonschema
 
 [options.package_data]
 * = *.json