fix verifyChanges causing 0: {, 1: } during insert and patch

[closertotheend]

Due to fact that most realtional dbs do not support string[] inside single column, people cast verifyChanges to text type. When field is deserialized from db we need to parse it twice. Otherwise Object.assign({}, '{}') will yield {0:'{', 1: '}'}

Related issue: https://github.com/feathersjs-ecosystem/feathers-authentication-management/issues/206