API response with `cafe_version` even when not in cafe mode

[andrewxhill]

https://github.com/textileio/go-textile/blob/master/core/api.go#L103

not sure the best way to go here, perhaps

cafe_version should be returned only when in cafe mode

api_version should be returned always (since the api is running).

or maybe they will always be the same, so just call it api_version

[andrewxhill]

Ah, okay. So this is the same number that is contained in the URL actually api/v0/ == cafe_version: 0. What I need here is more like the minor version so clients can uncover breaking changes a bit faster.

[sanderpick]

That would be node_version