Update MPFoundation.h (#541)
Update MPFoundation.h (#541)

Droping support for Xcode 6, adding support for Xcode 7.
mixpanel/mixpanel-iphone,carezone/mixpanel-iphone,mixpanel/mixpanel-iphone,mixpanel/mixpanel-iphone,carezone/mixpanel-iphone,mixpanel/mixpanel-iphone,mixpanel/mixpanel-iphone