Log Message:
py-dulwich: updated to 0.20.19

0.20.19
* Fix handling of negative matches in nested gitignores.

0.20.18
* Fix formatting in setup.py.
* Add release configuration.

0.20.17
* credentials: ignore end-of-line character.
* Fix failure in get_untracked_paths when the repository contains symlinks.
* docs: Clarify that Git objects are created on `git add`.

0.20.16
* Add flag to only attempt to fetch ignored untracked files when specifically \ 
requested.