Target 10.9 as minimal OSX version in all scripts, in order to match the libraries build script.
Differential Revision: https://code.wildfiregames.com/D1685
Tested By: trompetin17
Macos 10.8 was released in 2012. Considering how aggressive Mac is when it comes to upgrade and the fact people don't really know our game works on Mac I do not find it so hard to believe.
The good thing is now that my Dev environment works on 10.9 I can call the alarm.