Durably decorate instead of alias method

Was causing an issue where, in the event that file was loaded twice, it
would overrite the aliased method, so that the old update_cart was
infact the new method - causing an infinite loop.
Merge pull request #11 from Dkendal/no-loopy

Durably decorate instead of alias method
Merge pull request #12 from Dkendal/lost-cherry

@senjai :+1: this