All items have a `sell_in` value which denotes the number of days we have to sell the item. 
   All items have a `quality` value which denotes how valuable the item is
   At the end of each day our system lowers both values for every item by running the `update_quantity` method on each item. 

   Once the sell by date has passed, Quality degrades twice as fast
   The Quality of an item is never negative
   “Aged Brie” actually increases in Quality the older it gets
   The Quality of an item is never more than 50
   “Sulfuras, Hand of Ragnaros”, being a legendary item, never has to be sold or decreases in Quality
   “Backstage passes to a TAFKAL80ETC concert”, like aged brie, increases in `quality` as it’s `sell_in` value approaches; `quality` increases by 2 when there are 10 days or less and by 3 when there are 5 days or less but `quality` drops to 0 after the concert

We have recently signed a supplier of conjured items. This requires an update to our system:

   “Conjured Mana Cake” items degrade in Quality twice as fast as normal items

Task: Update the system to be able to handle "conjured" items. Failing specs have been added to help describe this behaviour.

You may assume that the test coverage is 100%. In otherwords, if the tests pass, the code is perfectly functional.

You may make any changes you'd like to the specs, but keep in mind that you shouldn't reduce coverage.