Bug: Add to_dict to RootLinterResult

[FragmentedPacket]

https://github.com/networktocode/yangify/blob/develop/yangify/linter/__init__.py#L167

Add to_dict method to RootLinterResult so it can be used within the NTC Rosetta CLI tools as well as any other tool/use that may want it.

Below is the link to the code in NTC Rosetta that uses it and then errors out:
https://github.com/networktocode/ntc-rosetta/blob/develop/ntc_rosetta/cli/print_processor.py#L32

Error:

File "/src/.venvs/ansible/lib64/python3.6/site-packages/ntc_rosetta/cli/print_processor.py", line 32, in print_parser
    text = json.dumps(lint.to_dict(), indent=4)
AttributeError: 'RootLinterResult' object has no attribute 'to_dict'