Log Message:
py-dateutil: updated to 2.8.1

Version 2.8.1:

Data updates
- Updated tzdata version to 2019c.

Bugfixes
- Fixed a race condition in the ``tzoffset`` and ``tzstr`` "strong" \ 
caches on
  Python 2.7.
- Parsing errors will now raise ``ParserError``, a subclass of ``ValueError``,
  which has a nicer string representation.
- ``parser.parse`` will now raise ``TypeError`` when ``tzinfos`` is passed a
  type that cannot be interpreted as a time zone. Prior to this change, it
  would raise an ``UnboundLocalError`` instead.
- Changed error message raised when when passing a ``bytes`` object as the time
  zone name to gettz in Python 3.
- Changed compatibility logic to support a potential Python 4.0 release.
- Updated many modules to use ``tz.UTC`` in favor of ``tz.tzutc()`` internally,
  to avoid an unnecessary function call.
- Fixed issue where ``dateutil.tz`` was using a backported version of
  ``contextlib.nullcontext`` even in Python 3.7 due to a malformed import
  statement.

Tests
- Switched from using assertWarns to using pytest.warns in the test suite.
- Fix typo in setup.cfg causing PendingDeprecationWarning to not be explicitly
  specified as an error in the warnings filter.
- Fixed issue where ``test_tzlocal_offset_equal`` would fail in certain
  environments (such as FreeBSD) due to an invalid assumption about what time
  zone names are provided.
- Fixed a minor bug in ``test_isoparser`` related to ``bytes``/``str``
  handling.
- Explicitly listed all markers used in the pytest configuration.
- Extensive improvements to the parser test suite, including the adoption of
  ``pytest``-style tests and the addition of parametrization of several test
  cases.
- Added tests for tzinfos input types.
- Fixed failure of test suite when changing the TZ variable is forbidden.
- Pinned all test dependencies on Python 3.3.

Documentation changes
- Fixed many misspellings, typos and styling errors in the comments and
  documentation.

Misc
- Added Python 3.8 to the trove classifiers.
- Moved as many keys from ``setup.py`` to ``setup.cfg`` as possible.
- Reorganized ``parser`` methods by functionality.
- Switched ``release.py`` over to using ``pep517.build`` for creating releases,
  rather than direct invocations of ``setup.py``.
- Added a "build" environment into the tox configuration, to handle \ 
dependency
  management when making releases.