Update meta-schema URIs before publishing draft 6

[handrews]

Currently the meta-schemas referenced in the validation and hyper-schema specs on master reference the Draft-04 meta-schemas (which are in fact the most recent published).

We need to update these before publishing these specs as draft 6. Since we cannot update the draft after publication, that means we MUST do these things in order just before submitting:

1. Put the draft-06 meta-schemas up on the web site
2. Update the specifications to the new meta-schema URIs
3. Submit specifications to IETF

[handrews]

Done and published!