Fix snapshot :shotengai_series

lib/shotengai/snapshot.rb

@@ -86,10 +86,11 @@ module Shotengai
     %i{
         title cover_image banners detail 
         original_price price 
-        shotengai_product
       }.each do |column|
       define_method(column) { super() || shotengai_series.send(column) }
     end
+    
+    delegate :shotengai_product, to: :shotengai_series
 
     def spec_value # Hash
       super() || shotengai_series.spec_value.decode