Handle new orientation enum value

I don't know what "unknown" orientation is, but there's a build warning now!

<img src="http://cl.ly/image/3h1C3D3U3n1y/Screen%20Shot%202014-09-22%20at%2016.35.16.png">
Merge pull request #22 from pnc/patch-3

Handle new iOS 8 orientation enum value