Remove milestone observer from db fixture.

db/fixtures/development/07_milestones.rb

-ActiveRecord::Base.observers.disable(:milestone_observer)
-
 Milestone.seed(:id, [
   { id: 1,  project_id: 1, title: 'v' + Faker::Address.zip_code },
   { id: 2,  project_id: 1, title: 'v' + Faker::Address.zip_code },
@@ -18,5 +16,3 @@ Milestone.all.map do |ml|
   ml.set_iid
   ml.save
 end
-
-ActiveRecord::Base.observers.enable(:milestone_observer)