dep ensure -n isn't actually a no-op

[pbennett]

Go 1.8 rc1 / osx
ensure -n is documented as a dry-run, but still does all the work, populating the vendor folder if it's not already there.
With no vendor/ directory present:

dep init
dep ensure -n
vendor/ is created as if -n was never specified.
Since there is no output normally, I'm assuming this is meant to be used alongside with the -v option.
(as of commit 1b193f4)

[rakyll]

To be clear, -n is doing nothing right. This needs to be implemented for ensure and remove.

[pbennett]

Correct, -n is basically being ignored and it's still running everything normally.

[carolynvs]

Is this a good candidate for me to pick up and take a crack at?

[sdboyer]

@carolynvs yeah, I think this should be a good one to pick up. Might be as simple as a single if statement :)