Fixed missing dependencies for iOS SDK 15.1

Summary: jadegordon found some missing dependencies. So, I added missing dependencies for new iOS SDK v15.1 inside FBUnityInterface.mm file

Reviewed By: joesus

Differential Revision: D41181740

fbshipit-source-id: 7c9bc7711cf96924c9f958de5e672896d997d060

UnitySDK/Assets/FacebookSDK/SDK/Editor/iOS/FBUnityInterface.mm

@@ -16,6 +16,8 @@
 // IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 // CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
+#import <SafariServices/SafariServices.h>
+#import <AuthenticationServices/AuthenticationServices.h>
 #import <FBSDKCoreKit/FBSDKCoreKit-Swift.h>
 #import <FBSDKLoginKit/FBSDKLoginKit-Swift.h>
 #import <Foundation/NSJSONSerialization.h>