infer download_root from XDG_CACHE_HOME if avail (#257)

whisper/__init__.py

@@ -90,7 +90,10 @@ def load_model(name: str, device: Optional[Union[str, torch.device]] = None, dow
     if device is None:
         device = "cuda" if torch.cuda.is_available() else "cpu"
     if download_root is None:
-        download_root = os.path.join(os.path.expanduser("~"), ".cache", "whisper")
+        download_root = os.getenv(
+            "XDG_CACHE_HOME", 
+            os.path.join(os.path.expanduser("~"), ".cache", "whisper")
+        )
 
     if name in _MODELS:
         checkpoint_file = _download(_MODELS[name], download_root, in_memory)