I apologize for any inconvenience. All development effort has moved to the layer-docker repository.
While we have strived to maintain charm compatibility with the layer-docker approach, there are some nuances that just wont be right. However for the intrepid, if you are certain you know what you are doing:
git clone https://github.com/juju-solutions/layer-docker
cd layer-docker
charm build
juju upgrade-charm docker --switch local:trusty/docker