DeprecationWarning / Draft4Validator.resolver is deprecated #68
Description
I've started seeing this deprecation warning when running jsonmerge:
opt/venv/lib/python3.11/site-packages/jsonmerge/__init__.py:27: DeprecationWarning: Accessing Draft4Validator.resolver is deprecated as of v4.18.0, in favor of the https://github.com/python-jsonschema/referencing library, which provides more compliant referencing behavior as well as more flexible APIs for customization.
self.resolver = merger.validator.resolver