First pass at "jitsu deploy"

@bradrydzewski Never written go before, but I think this should work. Haven't really used drone much either but will give it a shot locally sometime soon.

Let me know if you need anything else from me. Those should be the correct env vars. There is definitely more we could add:

- Deploy to a specific datacenter
- Always auto-increment a given version (minor, build, patch, etc)

... but this is a start!