version: bump version to rc6
version: bump version to rc6

Signed-off-by: Vincent Batts <d01a4772f0cffd3f005a7d7f01c59cd104c7a5fe@hashbangbash.com>

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