fix dependencies.tsv

turns out that if you do this:
GOOS=windows godeps -t ./... > dependencies.tsv
that you get the right dependencies, since windows dependencies are a strict
superset of linux dependencies.  This may not always be true, but it is right
now, and that's good enough for me.
This fixes bug https://bugs.launchpad.net/juju-core/+bug/1384818

http://reviews.vapour.ws/r/277/