Fix issue introduce in 38c4436e63c3449a68775839867bffa6faabe15e

An issue was introduce in commit 38c4436e63c3449a68775839867bffa6faabe15e The create callback fire after the save callback.

If you assign updated_at = created_at in save callback, created_at is nil because instanciate in create callback fire after.

So add this commit to fix this issue ( my bad ) or revert the commit 38c4436e63c3449a68775839867bffa6faabe15e