Facebook iOS SDK 3.18.1

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

Upgrading:
    https://developers.facebook.com/docs/ios/upgrading/
Facebook iOS SDK 3.18.2

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

Upgrading:
    https://developers.facebook.com/docs/ios/upgrading/
Merge commit 'ac9ad166739b1136b591014ae5c13176926b8cc8'

* commit 'ac9ad166739b1136b591014ae5c13176926b8cc8':
  Facebook iOS SDK 3.18.2
  Facebook iOS SDK 3.18.1