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:
#206

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[closertotheend]

Checked locally with npm link, fix seems to be working

[claustres]

Thanks for this as it seems to annoy many people. Not familiar enough with SQLite though to check if it's a valid workaround, but from a more general point of view I would ask if it would not be more "readable" and less risky (eg avoid any exception if user.verifyChanges is an empty string for some weird reason) with something like this (and ideally with a comment on the previous line to explain why we need it):
if (user.verifyChanges === '{}') ...

I will let run the tests anyway to ensure it works.