Fix deserialization of unit variants

[erickt]

serde_json allows for deserializing a unit variant like:

enum SomeEnum {
    SomeVariant
}

from either a string like "SomeVariant" or {"SomeVariant: null}. Previously serde_json5 would allow for any value in the second case. That data would then be thrown away. This changes serde_json5 to match serde_json and only allow null.

Note that this is a breaking change, and so it bumps the version.

[woody77]

Closes #10

[woody77]

This is going to merge-conflict with #6, right?

[coveralls]

Pull Request Test Coverage Report for Build 8788711153

Details

• 3 of 3 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.3%) to 91.605%

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Totals
Change from base Build 8759649977:	0.3%
Covered Lines:	622
Relevant Lines:	679

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💛 - Coveralls