Bump required Xcode to 5 to align with Chromium.
Bump required Xcode to 5 to align with Chromium.

https://www.chromium.org/dev/developers/how-tos/get-the-code
mentions that Xcode 5 or later is needed, we should require the same.

webrtc/webrtc-org,webrtc/webrtc-org,louquillio/webrtc-org,louquillio/webrtc-org,louquillio/webrtc-org,samdutton/webrtc-org,Scintillo/webrtc-org,webrtc/webrtc-org,samdutton/webrtc-org,Scintillo/webrtc-org,Scintillo/webrtc-org