Wrong class name in Motivation page in wiki

Near the bottom of the Factories section of the Motivation page in the wiki (https://github.com/google/guice/wiki/Motivation#factories), it refers to adding dependencies to `CreditCardFraudTracker`, when I think it should be `RealBillingService`. It's really small, but I was pretty confused for a couple of minutes looking for code that had `CreditCardFraudTracker` in it.