Don't strip proceeding hyphen (#4353)

* Don't strip proceeding hyphen

* Continue to strip whitespace

* Update multi_news.py

Co-authored-by: Quentin Lhoest <42851186+lhoestq@users.noreply.github.com>

Commit from https://github.com/huggingface/datasets/commit/b1d704d1cf2ccb6afbea7fc11421b5d7afeb2d78

multi_news.py

@@ -93,6 +93,5 @@ class MultiNews(datasets.GeneratorBasedBuilder):
                     # tokens "\n" are being replaced with "NEWLINE_CHAR". Here restore
                     # the natural newline token to avoid special vocab "NEWLINE_CHAR".
                     _DOCUMENT: src_line.strip().replace("NEWLINE_CHAR", "\n"),
-                    # Remove the starting token "- " for every target sequence.
-                    _SUMMARY: tgt_line.strip().lstrip("- "),
+                    _SUMMARY: tgt_line.strip(),
                 }