Support docker-py 1.2.1

[linlinlinlin]

docker-py 1.2.1 have been released yesterday.

How could we help to test it is work with compose 1.2 ?

[aanand]

1.2.0 and 1.2.1 seem to be missing from PyPi, but I'm already confident that Compose will work with them - several PRs (such as #1269) are using them via Git URL.

[dnephin]

We're on 1.3.1 now, so we can close this