Use dep

[arbourd]

Switch to golang/dep

Some between dep and glide:

• Cannot ignore golang.org/x/sys/unix (build fails as it doesn't import)
• dep vendors all dependencies when running dep ensure (for the time being) -- use dep prune to clean up unused dependencies
• unix builds are using dep at master -- i can download the binary in the Makefile instead

Closes #300

[CLAassistant]

All committers have signed the CLA.

[AppVeyorBot]

❌ Build torus-cli 383 failed (commit c4afffd46c by @arbourd)

[AppVeyorBot]

✅ Build torus-cli 386 completed (commit a1c544f6c1 by @arbourd)

[ianlivingstone]

This is awesome, thanks so much for the contribution!

[arbourd]

My pleasure. 🤓

Just a quick note: go list ./... | grep -v ./vendor shouldn't be needed with Go 1.9+ which automatically ignores the vendor folder.