change comment migration and change date_creation attribute for created_at

lib/orient_db/migrations/create_comment.rb

 class OrientDb::Migrations::CreateComment < OrientDb::Migration
 
   def up
-    create_class 'Comment', 'V' do |c|
-        c.property 'text', :string
-        c.property 'date_creation', :datetime
-        c.property 'last_modified', :datetime
+    create_class 'Comment', 'Object' do |c|
+      c.property 'text', :string
     end
   end
 

lib/orient_db/migrations/create_object.rb

@@ -3,7 +3,7 @@ class OrientDb::Migrations::CreateObject < OrientDb::Migration
   def up
     create_class 'Object', 'V' do |c|
         c.property 'name', :string
-        c.property 'date_creation', :datetime
+        c.property 'created_at', :datetime
         c.property 'last_modified', :datetime
     end
   end