[MODEL] Do not require models to respond to ancestors

Related: elastic#10, elastic#30, elastic#50, elastic#129, elastic#346

Author: miguelff

elasticsearch-model/lib/elasticsearch/model/adapters/active_record.rb

@@ -7,7 +7,7 @@ module Adapter
       module ActiveRecord
 
         Adapter.register self,
-                         lambda { |klass| !!defined?(::ActiveRecord::Base) && klass.ancestors.include?(::ActiveRecord::Base) }
+                         lambda { |klass| !!defined?(::ActiveRecord::Base) && klass.respond_to?(:ancestors) && klass.ancestors.include?(::ActiveRecord::Base) }
 
         module Records
           # Returns an `ActiveRecord::Relation` instance

elasticsearch-model/lib/elasticsearch/model/adapters/mongoid.rb

@@ -9,7 +9,7 @@ module Adapter
       module Mongoid
 
         Adapter.register self,
-                         lambda { |klass| !!defined?(::Mongoid::Document) && klass.ancestors.include?(::Mongoid::Document) }
+                         lambda { |klass| !!defined?(::Mongoid::Document) && klass.respond_to?(:ancestors) && klass.ancestors.include?(::Mongoid::Document) }
 
         module Records