Log Message:
py-pygit2: update to 0.28.1.

0.28.1 (2019-04-19)
-------------------------

- Now works with pycparser 2.18 and above
  `#846 <https://github.com/libgit2/pygit2/issues/846>`_

- Now ``Repository.write_archive(..)`` keeps the file mode
  `#616 <https://github.com/libgit2/pygit2/issues/616>`_
  `#898 <https://github.com/libgit2/pygit2/pull/898>`_

- New ``Patch.data`` returns the raw contents of the patch as a byte string
  `#790 <https://github.com/libgit2/pygit2/pull/790>`_
  `#893 <https://github.com/libgit2/pygit2/pull/893>`_

- New ``Patch.text`` returns the contents of the patch as a text string,
  deprecates `Patch.patch`
  `#790 <https://github.com/libgit2/pygit2/pull/790>`_
  `#893 <https://github.com/libgit2/pygit2/pull/893>`_

Deprecations:

- ``Patch.patch`` is deprecated, use ``Patch.text`` instead