Update zest.releaser to 6.22.1

[pyup-bot]

This PR updates zest.releaser from 6.18.1 to 6.22.1.

Changelog

6.22.1

-------------------

- When replacing new version in ``__version__ = "1.0"``, keep the existing quote style.
We always replaced double with single quotes, but now we keep them.
[graingert]

6.22.0

-------------------

- Fixed deadlock when communicating with git-lfs, or anything else that gives back lots of output.
[mcdeck]

- Fixed TypeError setting unicode in environment on Python 2.7 on Windows.
[mcdeck]

6.21.1

-------------------

- Fixed uploading to multiple servers if we do not want to upload to the first server.
Fixes `issue 357 <https://github.com/zestsoftware/zest.releaser/issues/357>`_.
[maurits]

6.21.0

-------------------

- Added support for Twine environment variables.
Especially, setting ``TWINE_REPOSITORY`` and ``TWINE_REPOSITORY_URL`` had no effect previously.
Fixes `issue 353 <https://github.com/zestsoftware/zest.releaser/issues/353>`_.
[mctwynne]

6.20.1

-------------------

- Added ``Dockerfile`` for much easier testing. See `the developer
documentation
<https://zestreleaser.readthedocs.io/en/latest/developing.html>`_. Previously,
getting the tests to run reliably locally was hard, now it is easy.
[Behoston]

6.20.0

-------------------

- Zest.releaser now sets an environment variable ``ZESTRELEASER`` so that
tools that we call on the command line can detect us. Don't depend on the
variable's textual content, just on the variable's name.

6.19.1

-------------------

- Percent signs (%) don't crash addchangelogentry anymore.

6.19.0

-------------------

- Do not go to the root of the repo by default.
When you were not in the root of a repo, ``zest.releaser`` already asked if you wanted to go there.
The default answer has now changed from yes to no.
This might help when releasing from monorepos.
Issue `326 <https://github.com/zestsoftware/zest.releaser/issues/326>`_.  [maurits]

6.18.2

-------------------

- Remove nothing_changed_yet line from history lines in unreleased section. [kleschenko]

Links

• PyPI: https://pypi.org/project/zest.releaser
• Changelog: https://pyup.io/changelogs/zest.releaser/
• Docs: https://zestreleaser.readthedocs.io