Why JSON % proc doesn't work for Enum?

[alexeypetrushin]

The `%` proc specifying how Enum should be converted to JSON doesn't work, why, 
and how to make it work?

[playground](https://play.nim-lang.org/#ix=2L9r)
    
    
    import json, re
    
    type SomeEnum* = enum SomeName, OtherName
    
    func `%`*(s: SomeEnum): JsonNode = %(($s).replace(re"Name$", ""))
    
    echo %SomeName
    echo @[SomeName]
    
    
    Run

Would produce
    
    
    "Some"
    @[SomeName]
    
    
    Run