Update project file deployment target to iOS 7 for 64-bit builds.

Reviewed By: chrisp

Test Plan: Built via XCode 5.
Facebook iOS SDK 3.9

Summary:
     see https://developers.facebook.com/ios/change-log-3.x/

Upgrading from 3.8
     https://developers.facebook.com/docs/ios/upgrading-from-3.8-to-3.9/

Reviewed By: jacl

Test Plan: Release Testing.

@update-submodule: vendor/OCMock