Update to latest JSON schema

[irm-codebase]

This issue was triggered by snakemake/snakemake#3299 (comment)

cffconvert seems to limit the top-most version of json schema: jsonschema >=3.0,<4
This is quite an old version of the spec, and limits the usability of cffconvert with other tools.

In particular, this does not support the (now fairly old) latest version of the JSON schema.

[kelly-sovacool]

Looks like @jspaaks has already done so (7a0b94b) but this change hasn't been released yet. It would be great to see a new release of cffconvert with this change!