Carthage update could give different results per run with Swift 4.2

It seems like the order in which dependencies are processed depends on the hash value of the dependency. Since hash values are stable with the current implementation of Swift and Carthage, this "undefined" order remains consistent across runs. However, Swift 4.2 will add random elements to default hashes, which means that the result of carthage update could be different across runs (see https://github.com/apple/swift-evolution/blob/master/proposals/0206-hashable-enhancements.md#proposed-solution).

A side benefit of providing a pre-defined order is it will be easier to create tests that exercise problems that will fail (or pass) consistently.