Update Info.plist

Fixes this issue: https://github.com/libgdx/packr/issues/19

However, CFBundleGetInfoString is still used by Finder, maybe it would be better to add a distinct configuration parameter to store the copyright information:
https://developer.apple.com/library/mac/documentation/MacOSX/Conceptual/BPFrameworks/Concepts/FrameworkAnatomy.html#//apple_ref/doc/uid/20002253-109555-BAJDHBCC