Update hack/vendor.sh to use libcontainer's update-vendor.sh script as the source of truth for libcontainer deps and not include them in Docker's repo twice

Signed-off-by: Andrew Page <admwiggin@gmail.com>
Update vendor with the updated canonical deps from libcontainer

Signed-off-by: Andrew Page <admwiggin@gmail.com>
Merge pull request #27 from tianon/update-libcontainer

Update hack/vendor.sh to use libcontainer's update-vendor.sh script as the source of truth for libcontainer deps and not include them in Docker's repo twice