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
* Kosmin/omniauth-verticalresponse#3

Author: pjg

lib/omniauth/strategies/constantcontact2.rb

@@ -5,11 +5,11 @@
 module OmniAuth
   module Strategies
     class ConstantContact2 < OmniAuth::Strategies::OAuth2
-      
+
       DEFAULT_RESPONSE_TYPE = 'code'
       DEFAULT_GRANT = 'authorization_code'
       API_PATH = 'https://api.constantcontact.com/v2'
-      
+
       option :name, "constantcontact"
 
       option :client_options, {
@@ -54,6 +54,10 @@ def raw_info
         }
         @raw_info ||= JSON.parse(access_token.get("#{API_PATH}/account/info", options).body)
       end
+
+      def callback_url
+        full_host + script_name + callback_path
+      end
     end
   end
 end