Match key names to correspond with filename
Thanks for the suggestion! I think the current checked-in `CHECKPOINT_URLS` is already not working. I believe anyone who tried using the new ckpts (`BLEURT-20-X`) can't unless this fix is in. The zip file from bleurt side unzips to directory name matching the filename (capitalized for new ones). For example without current changes I'd get the following error

```
---------------------------------------------------------------------------
AssertionError                            Traceback (most recent call last)
<ipython-input-5-f6832fe20f84> in <module>()
      1 predictions = ["hello there", "general kenobi"]
      2 references = ["hello there", "general kenobi"]
----> 3 bleurt = datasets.load_metric("bleurt", "bleurt-20")
      4 results = bleurt.compute(predictions=predictions, references=references)

4 frames
/usr/local/lib/python3.7/dist-packages/bleurt/checkpoint.py in read_bleurt_config(path)
     84   """Reads and checks config file from a BLEURT checkpoint."""
     85   assert tf.io.gfile.exists(path), \
---> 86       "Could not find BLEURT checkpoint {}".format(path)
     87   config_path = os.path.join(path, CONFIG_FILE)
     88   assert tf.io.gfile.exists(config_path), \

AssertionError: Could not find BLEURT checkpoint /root/.cache/huggingface/metrics/bleurt/bleurt-20/downloads/extracted/e34c60f1a05394ecda54e253a10413ca7b5d59f9a23f3cc73258c6b78ffa2f50/bleurt-20
```
inspecting specified path I see that directory name is `BLEURT-20` instead of `bleurt-20`. 
Other solution similar to your suggestion is meddle with `dl_manager.download_and_extract` to unzip to paths with lowering all the paths but I imagine this will affect other parts of the library. 
In order to properly locate downloaded ckpt files key name needs to match filename. Correcting change introduced in #3235 