update github.com/fsouza/go-dockerclient

One line change in ``pkg/kubelet/kubelet.go``.
No. It's not docker's problem. Docker use int64 for anything related to memory. Not sure why they changed it.

We used int64 in cAdvisor, but it failed in some cases because if the memory is unlimited, it will return 2^64 (max. value for uint64), so we changed to uint64 in cAdvisor. I'm not sure if this is the reason why they changed to float64.