Fix compatibility with omniauth-oauth 1.4+

References:
* omniauth/omniauth-oauth2#70
* omniauth/omniauth-oauth2@2615267
* omniauth/omniauth-oauth2#82
* jdennes/omniauth-createsend#3
* WebTheoryLLC/omniauth-twitch#4
* jdennes/omniauth-createsend#5
* DripEmail/omniauth-drip#6

lib/omniauth/strategies/verticalresponse.rb

@@ -10,11 +10,14 @@ class Verticalresponse < OmniAuth::Strategies::OAuth2
  token_url: 'api/v1/oauth/access_token'
  }
  option :provider_ignores_state, true
- 
+
  uid do
  access_token.params['user_id']
  end
 
+ def callback_url
+ full_host + script_name + callback_path
+ end
  end
  end
 end