[ci skip][docs] Keep Product model associations consistent

Author: excid3

guides/source/getting_started.md

@@ -2261,9 +2261,9 @@ emails anytime the inventory count changes from 0 to a positive number.
 
 ```ruby#9-19
 class Product < ApplicationRecord
+  has_many :subscribers, dependent: :destroy
   has_one_attached :featured_image
   has_rich_text :description
-  has_many :subscribers, dependent: :destroy
 
   validates :name, presence: true
   validates :inventory_count, numericality: { greater_than_or_equal_to: 0 }