Command seems broken

[remicollet]

$ grep -ri RefResolver .
./bin/validate-json:$refResolver = new JsonSchema\RefResolver($retriever, $resolver);
./bin/validate-json:$schema = $refResolver->resolve($urlSchema);

But this class didn't exists in 4.x version, so:

PHP Fatal error: Uncaught Error: Class 'JsonSchema\RefResolver' not found