added support for environ to manage github auth locally

[Environ](https://github.com/weavejester/environ) simplifies management of env vars as data, I think, and avoids hardcoding basic auth in api clients. I'd like to push this as a best practice.

The following api pulls :gh-username and :gh-password from ~/.lein/profiles.clj or .lein-env map and returns a string <username:password>, as requiured by tentacles.

`(users/me {:auth (environ-auth)}`

I also updated the clojure version.