Adds tests for non zero-padded dates

[helrond]

As outlined in IETF RFC 3559, section 5.6, dates should follow the format YYYY-MM-DD, so days or months that are non-zero padded should be invalid.

The date format was introduced in Draft7 of JSON Schema, so I've only added the tests for that version and 2019-09.

[Julian]

Thanks again, this is great. One thing we probably should do at the same time is have a look at the date-time tests -- probably these same two tests should be added there as part of the full date-time validation (that YYYY-M-D doesn't pass there either, assuming that's correct behavior there)

[karenetheridge]

you missed draft3, draft4, and draft6 :)

[helrond]

@karenetheridge the date format was not introduced until draft7, which Is why draft3, draft4 and draft6 have not been changed.

[karenetheridge]

ah, I see, date was present in draft3 but left out of 4 and 6.

date-time is present in all drafts from 3 to the present.

[Julian]

Fantastic. Think this looks good! Merging.