Log Message:
py-dulwich: updated to 0.19.10

0.19.10:
IMPROVEMENTS
* Add dulwich.porcelain.write_tree.
* Support reading MERGE_HEADS in Repo.do_commit.
* Import from collections.abc rather than collections where
  applicable. Required for 3.8 compatibility.
* Support plain strings as refspec arguments to
  dulwich.porcelain.push.
* Add support for creating signed tags.

BUG FIXES
*  Handle invalid ref that pretends to be a sub-folder under a valid ref.