Fix error with zst compressed files

They can exist alone without a tar.

Signed-off-by: Philippe Ombredanne <pombredanne@nexb.com>

Author: pombredanne

src/extractcode/archive.py

@@ -799,7 +799,7 @@ def try_to_extract(location, target_dir, extractor):
     name='zstd',
     filetypes=('zstandard compressed',),
     mimetypes=('application/x-zstd',) ,
-    extensions=('.tar.zst', '.tar.zstd',),
+    extensions=('.zst', '.zstd',),
     kind=regular_nested,
     extractors=[extract_zstd],
     strict=False