JSon instances for Map/Set require Ord constraint

[bladyjoker]

https://github.com/mlabs-haskell/lambda-buffers/blob/f5acbc09718191cdfbf374ee5aaeacf626b8b9e9/runtimes/haskell/lbr-prelude/src/LambdaBuffers/Runtime/Prelude/Json.hs#L140

sum X = Y | Z
derive Json X

record Test  = {
  test : Map X Integer
}
derive Json Test

The generated code will break because X doesn't have Ord.

See #224