Fix Logspout Under Docker Machine

[hkeeler]

With the switch from boot2docker to docker-machine, the logspout container now fails with a:

logspout_1 | 2015/11/13 17:32:33 pump ended: dial unix /var/run/docker.sock: connection refused

It seems related to the issue described here:

• https://github.com/jwilder/nginx-proxy/issues/113