Update plumbum to 1.7.1

[pyup-bot]

This PR updates plumbum from 1.6.8 to 1.7.1.

Changelog

1.7.0

-----

* Commands: support ``.with_cwd()`` (`513 <https://github.com/tomerfiliba/plumbum/pull/513>`_)
* Commands:  make ``iter_lines`` deal with decoding errors during iteration (`525 <https://github.com/tomerfiliba/plumbum/pull/525>`_)
* Commands: fix handling of env-vars passed to plumbum BoundEnvCommands  (`513 <https://github.com/tomerfiliba/plumbum/pull/513>`_)
* Commands: fix support for win32 in ``iter_lines`` (`500 <https://github.com/tomerfiliba/plumbum/pull/500>`_)
* Paths: fix incorrect ``__getitem__`` method in Path (`506 <https://github.com/tomerfiliba/plumbum/pull/506>`_)
* Paths: Remote path stat had odd OSError  (`505 <https://github.com/tomerfiliba/plumbum/pull/505>`_)
* Paths: Fix ``RemotePath.copy()`` (`527 <https://github.com/tomerfiliba/plumbum/pull/527>`_)
* Paths: missing ``__fspath__`` added (`498 <https://github.com/tomerfiliba/plumbum/pull/498>`_)
* SSH: better error reporting on SshSession error (`515 <https://github.com/tomerfiliba/plumbum/pull/515>`_)
* Internal: redesigned CI, major cleanup to setuptools distribution, Black formatting, style checking throughout.

1.6.9

-----

* Last version to support Python 2.6; added python_requires for future versions (`507 <https://github.com/tomerfiliba/plumbum/pull/507>`_)
* Paths: Fix bug with subscription operations (`498 <https://github.com/tomerfiliba/plumbum/pull/498>`_), (`#506 <https://github.com/tomerfiliba/plumbum/pull/506>`_)
* Paths: Fix resolve (`492 <https://github.com/tomerfiliba/plumbum/pull/492>`_)
* Commands: Fix resolve (`491 <https://github.com/tomerfiliba/plumbum/pull/491>`_)
* Commands: Add context manager on popen (`495 <https://github.com/tomerfiliba/plumbum/pull/495>`_)
* Several smaller fixes (`500 <https://github.com/tomerfiliba/plumbum/pull/500>`_), (`#505 <https://github.com/tomerfiliba/plumbum/pull/505>`_)

Links

• PyPI: https://pypi.org/project/plumbum
• Changelog: https://pyup.io/changelogs/plumbum/
• Docs: https://plumbum.readthedocs.io

[pyup-bot]

Closing this in favor of #677