enable callbacks for specs after notification

spec/services/notification_service_spec.rb

@@ -2,7 +2,8 @@ require 'spec_helper'
 describe NotificationService do
   # Disable observers to prevent factory trigger notification service
-  before { ActiveRecord::Base.observers.disable :all }
+  before(:all) { ActiveRecord::Base.observers.disable :all }
+  after(:all) { ActiveRecord::Base.observers.enable :all }
   let(:notification) { NotificationService.new }