Fixed createUserWithEmail local error

Author: auser

ios/Firestack/FirestackAuth.m

@@ -215,7 +215,7 @@ - (Boolean) listeningForAuth {
              NSDictionary *err = @{
                                    @"error": @"createUserWithEmailError",
                                    @"name": @([error code]),
-                                   @"description": [error description]
+                                   @"description": [error localizedDescription]
                                    };
              callback(@[err]);
          }