`download-artifacts` does not work

[benbuckman]

Running circle download-artifacts <build number>, I see one of the following happen:

1. On a build with a small number of artifacts, it says it's downloading them to a tmp folder, but the folder is actually empty.

2. On a build with a very large number of artifacts, it hits an error with too many concurrent connections.

3. Today on master, with any build number, I'm getting

json: cannot unmarshal object into Go value of type []*circle.CircleArtifact

None of these are the desired behavior.

[benbuckman]

@kevinburke Would you be interested in fixing this? Do you use this anymore?

[ianmdawson]

@benbuckman you were able to figure this out, correct?