Update dependencies to work with new layer media type

[glestaris]

Since opencontainers/image-spec#347 the layer media type has been changed. This commit bumps the image-spec and dependencies.

[wking]

On Tue, Oct 25, 2016 at 01:43:45PM -0700, George Lestaris wrote:

M vendor/github.com/opencontainers/runtime-spec/specs-go/config.go (44)
M vendor/github.com/opencontainers/runtime-spec/specs-go/state.go (2)
M vendor/github.com/opencontainers/runtime-spec/specs-go/version.go (2)

Can we pin runtime-spec in glide.yaml? I don't think the current repo
is stable enough to leave our dependency floating (with
incompatible-Go changes between Go changes breaking the current
patch-level comparison [1,2]). And the runtime-spec versions are
versioning the config format anyway (opencontainers/runtime-spec#523),
so we shouldn't expect them to apply to the Go bindings.

[runcom]

is this a duplicate of #69 ?

[wking]

Yes.

[glestaris]

I'll close this one since #69 seems to work better with @wking's request :)