fix: Migration primary_key_type nil-safety

Author: blocknotes

db/migrate/20200702202022_create_active_storage_db_files.rb

@@ -20,7 +20,6 @@ def change
 
   def primary_key_type
     config = Rails.configuration.generators
-    primary_key_type = config.options[config.orm][:primary_key_type]
-    primary_key_type || :primary_key
+    config.options.dig(config.orm, :primary_key_type) || :primary_key
   end
 end