update github.com/fsouza/go-dockerclient

One line change in ``pkg/kubelet/kubelet.go``.
Thanks for looking into it, happy docker didn't change that. Maybe we can file an issue with fsouza/go-dockerclient? I'm OK with updating as long as we're working to make sure it doesn't stay this way. Maybe you can add a // TODO: persuade dockerclient to go back to int64 or uint64 representation?