Syntax error when emitting to JSON from a YAML zero leading number value

[captain-yoshi]

Emitting a JSON file from a YAML with a leading zero value will give a SyntaxError when parsed in JSON.

YAML

error: 04

JSON

{"error": 04}

Not sure if the responsibility is on the user or the library. Not sure if it's easy but when emitting to JSON you could convert to a string if there is a leading zero number, as it is invalid in JSON.