Defining :original for add_configuration_line

Responding to warning

[1;32mDeface:[0m 4 overrides found for 'spree/admin/shared/_configuration_menu'
[1;32mDeface:[0m 'add_configuration_line' matched 1 times with '[data-hook='admin_configurations_sidebar_menu'], #admin_configurations_sidebar_menu[data-hook]'
[1;32mDeface: [WARNING][0m No :original defined for 'add_configuration_line', you should change its definition to include:
 :original => 'db886cb54ef1ca8a8284ab170ec7e19788d28259'

Fixes #72