Add configuration option to set resource type to singular/plural with jsonapi.

lib/active_model/serializer.rb

@@ -135,7 +135,11 @@ module ActiveModel
     end
 
     def json_api_type
-      object.class.model_name.plural
+      if config.jsonapi_resource_type == :plural
+        object.class.model_name.plural
+      else
+        object.class.model_name.singular
+      end
     end
 
     def attributes(options = {})

lib/active_model/serializer/configuration.rb

@@ -7,6 +7,7 @@ module ActiveModel
       included do |base|
         base.config.array_serializer = ActiveModel::Serializer::ArraySerializer
         base.config.adapter = :flatten_json
+        base.config.jsonapi_resource_type = :plural
       end
     end
   end