Always expose the refresh_token
Always expose the refresh_token

Twitch API fails to provide an `expires_in` attribute in their authentication response,
which causes omniauth-oauth2 gem to ignore the refresh token
(see https://github.com/omniauth/omniauth-oauth2/issues/122).

We override the `credentials` block to remove the check for expiration attribute.

WebTheoryLLC/omniauth-twitch