Bugfix: Fix purchase-item fn in chapter04
Bugfix: Fix purchase-item fn in chapter04

josiahcarlson/redis-in-action,josiahcarlson/redis-in-action,josiahcarlson/redis-in-action,josiahcarlson/redis-in-action,josiahcarlson/redis-in-action,josiahcarlson/redis-in-action