Conflicts with docker package used by docker-compose

[nhumrich]

I would assume its pretty common for both xonsh (and its docker completions) and docker-compose to both be installed "on the system" and not in an virtual env. However, docker-compose uses the docker package on pypi, but this library uses docker-py. The two conflict with eachother and make it so you can either have completions, or docker-compose, but not both.

It would be great to update this to use the docker package instead of docker-py so that the two dont conflict.