mediatype of layers should be application/vnd.oci.image.layer.v1.tar+gzip
mediatype of layers should be application/vnd.oci.image.layer.v1.tar+gzip

Signed-off-by: Vanessa Sochat <9c1581d433637ebb0bd02436a7140331ccd16cb6@stanford.edu>

opencontainers/image-spec,opencontainers/image-spec,jonboulle/image-spec,jonboulle/image-spec