Missing ability to refresh token

I don't see a way to refresh the OAuth token once it has expired. The `#connect_oauth` function only accepts the original token, which appears to expire after a few hours. The standard OAuth handshake, and credentials provided by `omniauth-heroku` include a `refresh_token` attribute which may be used to automatically obtain a new token one it has expired. It would be nice if this gem accepted the `refresh_token` as a param (or if it already does, document it somehow. I don't see anything in the gem docs here or in heroic.), and could automatically do the refreshed token exchange.