travis: upgrade Go 1.6 to rc2
travis: upgrade Go 1.6 to rc2

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