`Json.stringify` in sdk-js is different from `str(object)` in python.

[posgnu]

Json.stringify in sdk-js is different from str(object) in python. As a result, metadata in assetscheme can be different when the assetscheme is minted from sdk-js and sdk-python. It might not be a problem in each SDK's functionality but it can ruin a consistency between SDKs.