message: test(http): fix Body.concat test
diff: @@ -126,7 +126,7 @@ fn test_body_stream_concat() {
  tx.send(Ok("world".into())).wait().unwrap();
  });
  - let total = body.concat2().wait().unwrap();
  + let total = body.concat().wait().unwrap();
  assert_eq!(total.as_ref(), b"hello world");
  }
  