GCM Mac sample project doesn't compile in Xcode 7.2

[bendinwire]

Title says it all.

Downloading latest version, then running the Mac target produces 12 errors and three warnings.

Does it compile for anyone else?

[danoli3]

#68

This pull request fixes this. (Or you can also just uncheck the GCMMuliplayer.m from the OSX Target to compile)

[kingsNow]

I use two mobile phones to test. In GameCenter, they can only see their own scores. In your demo is the number of players can see the ranking, in my own project can only see their own scores. Thanks!