Can break with change of deps with same name

[mxcl]

If you run this script:

import DeckOfPlayingCards  // apple/example-package-deckofplayingcards ~> 3.0.0
import PlayingCard
import Cycle  // @NSHipster == master

Then this:

import DeckOfPlayingCards // @NSHipster ~> 4.0.0
import PlayingCard
import Cycle // @NSHipster == bb11e28

It will fail because the Package.resolved contains the old package url, and doesn't update. Could be a bug in SwiftPM, but either way we should figure out what to do about a workaround.