Update docker-py

From https://github.com/bfirsh/docker-py/commit/0a9512d008b4b79d625aed360d9dc323ccc342d5
Add link alias without project name

REDIS_1_PORT_6379_TCP_ADDR instead of
FIGTEST_REDIS_1_PORT_6379_TCP_ADDR.

Ref #37
Merge pull request #54 from orchardup/add-link-alias-without-project-name

Add link alias without project name