Update spec support to version draft-wright-json-schema-validation-01
http://json-schema.org/latest/json-schema-validation.html#rfc.appendix.B
I don’t think it makes sense to support the old versions of the schema, since they’re all drafts so far.
There will probably be more updates to the schema in future (it’s still a draft). We should document which version we support (we currently support draft-fge-json-schema-validation-01).