CI: require a sufficiently-recent JSON-Schema

ci/configvalidator.py

@@ -45,6 +45,7 @@ ERR_IMPORT, ERR_USAGE, ERR_FILE_NOT_FOUND, ERR_SYNTAX, ERR_INVALID = range(1,6)
 #
 try:
     from jsonschema import validate, SchemaError, ValidationError
+    from jsonschema import draft7_format_checker
     from yaml import safe_load, YAMLError
 except ImportError as e:
     print(e)