travis-script: start docker after install
travis-script: start docker after install

Should fix the build with Docker 1.12.0.

davidstack/go-dockerclient,paulbellamy/go-dockerclient,tarsisazevedo/go-dockerclient,davidstack/go-dockerclient,csrwng/go-dockerclient,tarsisazevedo/go-dockerclient,fsouza/go-dockerclient,csrwng/go-dockerclient