loop update could be update_all

app/controllers/application_controller.rb
```
129    session_cart.cart_items.each do |item|
130      item.update_attribute(:user_id, user.id ) if item.user_id != user.id
131   end
```
replaced by update_all
```
session_cart.cart_items.where.not(user_id: user.id).update_all(user_id: user.id)
```