Upgraded to SBJson 3.1.1

Considering the frequent conflicts with Facebook-iOS-SDK's SBJson and other libraries, and given the rise of CocoaPods, we should consider upgrading Facebook-iOS-SDK's internal SBJson to a modern version (or using JSONKit).

In this pull request, I've upgraded SBJson from v2.2.3 to v3.1.1 for Facebook-iOS-SDK v3.0.7.

Reference:
[Facebook-iOS-SDK in CocoaPods](https://github.com/CocoaPods/Specs/tree/master/Facebook-iOS-SDK)
See #296, #338, #419, #431, #438, #443, #455, #467, #471 for previous discussions on the issue.