Bump go-dockerclient.
Merge pull request #250 from plietar/master

Bump go-dockerclient.
Supporting graceful signal shutdown.

Adding a signal handler and gracefully shutting down all threads.
Merge pull request #251 from vmarmol/shutdown

Supporting graceful signal shutdown.
Also handle SIGTERM.
Merge pull request #253 from vmarmol/shutdown

Also handle SIGTERM.