Step: Pulling necessary etcd Docker image hangs

This step in `install-k8s-master.sh` seems to just hang for me... I am walking through each step in the install script once I attempt to pull this on this socket it seems to just hang... Is there something I'm missing?
```
root@pi-1:~/k8s-on-rpi-master# docker -H unix:///var/run/docker-bootstrap.sock pull andrewpsuedonym/etcd:2.1.1
```