Log Message:
py-pygit2: update to 0.27.1.

0.27.1 (2018-06-02)
-------------------------

Breaking changes:

- Now ``discover_repository`` returns ``None`` if repository not found, instead
  of raising ``KeyError``
  `#531 <https://github.com/libgit2/pygit2/issues/531>`_

Other changes:

- New ``DiffLine.raw_content``
  `#610 <https://github.com/libgit2/pygit2/issues/610>`_

- Fix tests failing in some cases
  `#795 <https://github.com/libgit2/pygit2/issues/795>`_

- Automatize wheels upload to pypi
  `#563 <https://github.com/libgit2/pygit2/issues/563>`_