Rename CallbackRunner to CallbacksObserver since it's an observer

lib/factory_girl.rb

@@ -18,7 +18,7 @@ require 'factory_girl/evaluator'
 require 'factory_girl/evaluator_class_definer'
 require 'factory_girl/attribute'
 require 'factory_girl/callback'
-require 'factory_girl/callback_runner'
+require 'factory_girl/callbacks_observer'
 require 'factory_girl/declaration_list'
 require 'factory_girl/declaration'
 require 'factory_girl/sequence'

lib/factory_girl/callbacks_observer.rb

@@ -1,5 +1,5 @@
 module FactoryGirl
-  class CallbackRunner
+  class CallbacksObserver
     def initialize(callbacks, evaluator)
       @callbacks = callbacks
       @evaluator = evaluator

lib/factory_girl/factory.rb

@@ -36,7 +36,7 @@ module FactoryGirl
       attribute_assigner = AttributeAssigner.new(evaluator, build_class, &instance_builder)
 
       evaluation = Evaluation.new(attribute_assigner, to_create)
-      evaluation.add_observer(CallbackRunner.new(callbacks, evaluator))
+      evaluation.add_observer(CallbacksObserver.new(callbacks, evaluator))
 
       strategy.result(evaluation).tap(&block)
     end