Update dolma.py

When loading data from _DATA_DIR, this line caused an FileNotFoundError due to an incorrect path.

dolma.py

@@ -112,7 +112,7 @@ class Dolma(datasets.GeneratorBasedBuilder):
             subset_urls = f.read().splitlines()
 
         if _DATA_DIR is not None:
-            subset_files = [os.path.join(_DATA_DIR, url.replace(_BASE_URL, "").lstrip("/")) for url in subset_urls]
+            subset_files = [os.path.join(_DATA_DIR, os.path.basename(url)) for url in subset_urls]
         else:
             subset_files = dl_manager.download(subset_urls)