changed the format of "id" to "uri-reference"

According to the JSON schema spec (draft 4, Section 7.1)[http://json-schema.org/latest/json-schema-core.html#rfc.section.7.1], ids should be URI References, not URIs. This is supported by the examples given in the spec and in other parts of this metaschema, since things like "#schema1" and "#/definitions/schemaArray" are not URIs according to (RFC 2396)[http://www.ietf.org/rfc/rfc2396.txt] but are URI References.