updates the Calabash::Cucumber::Device class for Xcode 5 and iOS 7

* adds `ios7?` method
* fixes `iphone_5?` method for Xcode 5 simulator (device syntax changed)

this fix is compatible with Xcode 4 simulator(s) and devices.

NOT TESTED ON physical iPhone 5 - i don't have one.  if you send me one, i will do this test. :)