Fix iOS auth exception

Author: chrisbianca

ios/Firestack/FirestackAuth.m

@@ -137,7 +137,7 @@ @implementation FirestackAuth
                                              sendJSEvent:AUTH_CHANGED_EVENT
                                              props: @{
                                                       @"eventName": @"userTokenError",
-                                                      @"msg": [error localizedFailureReason]
+                                                      @"msg": [error localizedDescription]
                                                       }];
                                         } else {
                                             [self