Fix the foreign_key name

db/migrate/1_create_shotengai_products_and_orders.rb

@@ -28,7 +28,7 @@ class CreateShotengaiProductsAndOrders < ActiveRecord::Migration[5.1]
       t.string :type
       t.json :meta
 
-      t.references :shotengai_products, foreign_key: true
+      t.references :shotengai_product, foreign_key: true
 
       t.timestamps
     end
@@ -72,7 +72,7 @@ class CreateShotengaiProductsAndOrders < ActiveRecord::Migration[5.1]
       t.json :meta
 
       t.references :shotengai_series, foreign_key: true
-      t.references :shotengai_orders, foreign_key: true
+      t.references :shotengai_order, foreign_key: true
 
       t.timestamps
     end

lib/shotengai/series.rb

@@ -10,7 +10,7 @@ module Shotengai
   #  spec                  :json
   #  type                  :string(255)
   #  meta                  :json
-  #  shotengai_products_id :integer
+  #  shotengai_product_id :integer
   #  created_at            :datetime         not null
   #  updated_at            :datetime         not null
   #

lib/shotengai/snapshot.rb

@@ -14,7 +14,7 @@ module Shotengai
   #  type                :string(255)
   #  meta                :json
   #  shotengai_series_id :integer
-  #  shotengai_orders_id :integer
+  #  shotengai_order_id :integer
   #  created_at          :datetime         not null
   #  updated_at          :datetime         not null
   #