Some dependencies seem to not get vendored

[karalabe]

I've got the following library: https://github.com/karalabe/deepstream. If I run trash --update && trash, for some reason the github.com/docker/go-connections/nat package is not detected as a dependency, which will result in a build failure:

$ go test -v
# github.com/karalabe/deepstream
package github.com/karalabe/deepstream (test)
	imports github.com/fsouza/go-dockerclient
	imports github.com/docker/docker/api/types/swarm
	imports github.com/docker/docker/api/types/container
	imports github.com/docker/go-connections/nat: cannot find package "github.com/docker/go-connections/nat" in any of:
[...]