File path error when evaluating on RefCOCOp

I got and `OSError: No such file or directory` when evaluating on RefCOCOp, which seems to be caused by the inconsistency between [line 37](https://github.com/allenai/gpv-1/blob/4a5c1f212d115d4146bab2a691ce40fc07de4222/exp/gpv/compute_predictions.py#L37) and [line164](https://github.com/allenai/gpv-1/blob/4a5c1f212d115d4146bab2a691ce40fc07de4222/exp/gpv/compute_predictions.py#L164). I solved this problem by change line 37 and line 38 to the following code

```py
boxes_h5py = h5py.File(os.path.join(
eval_dir,f'{cfg.eval.task}_{cfg.task_configs.data_split}_{cfg.eval.subset}_boxes.h5py'),'w')
```

## Command

command to reproduce the error

```sh
# Set up env and prepare data following guidance, here I set the `download_coco_test_images` to False

# Evaluate
bash exp/gpv/scripts/eval.sh gpv_coco_sce RefCocop val '' ${work_dir}/GPV/exp_output ${work_dir}/GPV

```