The $id ref of the json schema is wrong

[andersjaensson]

The $id field of the json schema points to "http://github.com/manfred/mac/schema.json" which does not seem to be correct?

See https://github.com/getmanfred/mac/blob/e7d77cd05711d13c5e014c03cb84b341e3e1c244/schema/schema.json#L3