Fix Spree::OrderWalkthrough.up_to to not transition past the action

* Previously specifying :address, or any other state, will cause this
  method to transition to the *next* action after it. I believe, based
  on the name of the method, this is incorrect. It is the intention of
  someone using this method to transition to the specific state they
  specified, not whatever comes after it.
Merge pull request #35 from MountainRoseHerbs/2-3-stable-mrh-fix-order-walkthrough

Fix Spree::OrderWalkthrough.up_to to not transition past the action