Fix failing specs on local machine [fix #1023]

Since the structure of Node returned by ActiveReocrd changed from 54de9b1,
the spec execution failed.

refs: rails/rails@54de9b1

lib/ransack/adapters/active_record/context.rb

@@ -186,6 +186,8 @@ def extract_correlated_key(join_root)
             correlated_key = correlated_key.left.left
           elsif correlated_key.is_a? Arel::Nodes::Equality
             correlated_key = correlated_key.left
+          elsif correlated_key.is_a? Arel::Nodes::Grouping
+            correlated_key = join_root.right.expr.right.left
           else
             correlated_key
           end

spec/ransack/search_spec.rb

@@ -238,9 +238,9 @@ module Ransack
         real_query = remove_quotes_and_backticks(s.to_sql)
 
         expect(real_query)
-          .to include "LEFT OUTER JOIN articles ON articles.person_id = people.id"
+          .to match(%r{LEFT OUTER JOIN articles ON (\('default_scope' = 'default_scope'\) AND )?articles.person_id = people.id})
         expect(real_query)
-          .to include "LEFT OUTER JOIN articles articles_people ON articles_people.person_id = parents_people.id"
+          .to match(%r{LEFT OUTER JOIN articles articles_people ON (\('default_scope' = 'default_scope'\) AND )?articles_people.person_id = parents_people.id})
         expect(real_query)
           .to include "people.name = 'person_name_query'"
         expect(real_query)