Bump python-dateutil from 2.6.0 to 2.8.1

[dependabot-preview]

Bumps python-dateutil from 2.6.0 to 2.8.1.

Release notes

Sourced from python-dateutil's releases.

2.8.1

Version 2.8.1 (2019-11-03)

Data updates

• Updated tzdata version to 2019c.

Bugfixes

• Fixed a race condition in the tzoffset and tzstr "strong"
  caches on Python 2.7. Reported by [@​kainjow](https://github.com/kainjow) (gh issue #901).
• Parsing errors will now raise ParserError, a subclass of
  ValueError, which has a nicer string representation. Patch by
  [@​gfyoung](https://github.com/gfyoung) (gh pr #881).
• 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. Patch by
  [@​jbrockmendel](https://github.com/jbrockmendel) (gh pr #891).
• Changed error message raised when when passing a bytes object as
  the time zone name to gettz in Python 3. Reported and fixed by
  [@​labrys](https://github.com/labrys) () (gh issue #927, gh pr #935).
• Changed compatibility logic to support a potential Python 4.0
  release. Patch by Hugo van Kemenade (gh pr #950).
• Updated many modules to use tz.UTC in favor of tz.tzutc()
  internally, to avoid an unnecessary function call. (gh pr #910).
• Fixed issue where dateutil.tz was using a backported version of
  contextlib.nullcontext even in Python 3.7 due to a malformed
  import statement. (gh pr #963).

Tests

• Switched from using assertWarns to using pytest.warns in the test
  suite. (gh pr #969).
• Fix typo in setup.cfg causing PendingDeprecationWarning to not be
  explicitly specified as an error in the warnings filter. (gh pr
  #966)
• 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. Reported and fixed by Kubilay
  Kocak (gh issue #918, pr #928).
• Fixed a minor bug in test_isoparser related to bytes/str
  handling. Fixed by [@​fhuang5](https://github.com/fhuang5) (gh issue #776, gh pr #879).
• Explicitly listed all markers used in the pytest configuration. (gh
  pr #915)
• Extensive improvements to the parser test suite, including the
  adoption of pytest-style tests and the addition of parametrization

... (truncated)

Changelog

Sourced from python-dateutil's changelog.

Version 2.8.1 (2019-11-03)

Data updates

• Updated tzdata version to 2019c.

Bugfixes

• Fixed a race condition in the tzoffset and tzstr "strong" caches on
  Python 2.7. Reported by @​kainjow (gh issue #901).
• Parsing errors will now raise ParserError, a subclass of ValueError,
  which has a nicer string representation. Patch by @​gfyoung (gh pr #881).
• 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. Patch by @​jbrockmendel (gh pr
  #891).
• Changed error message raised when when passing a bytes object as the time
  zone name to gettz in Python 3. Reported and fixed by @​labrys () (gh issue
  #927, gh pr #935).
• Changed compatibility logic to support a potential Python 4.0 release. Patch
  by Hugo van Kemenade (gh pr #950).
• Updated many modules to use tz.UTC in favor of tz.tzutc() internally,
  to avoid an unnecessary function call. (gh pr #910).
• Fixed issue where dateutil.tz was using a backported version of
  contextlib.nullcontext even in Python 3.7 due to a malformed import
  statement. (gh pr #963).

Tests

• Switched from using assertWarns to using pytest.warns in the test suite. (gh
  pr #969).
• Fix typo in setup.cfg causing PendingDeprecationWarning to not be explicitly
  specified as an error in the warnings filter. (gh pr #966)
• 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. Reported and fixed by Kubilay Kocak (gh issue #918,
  pr #928).
• Fixed a minor bug in test_isoparser related to bytes/str
  handling. Fixed by @​fhuang5 (gh issue #776, gh pr #879).
• Explicitly listed all markers used in the pytest configuration. (gh pr #915)
• Extensive improvements to the parser test suite, including the adoption of
  pytest-style tests and the addition of parametrization of several test
  cases. Patches by @​jbrockmendel (gh prs #735, #890, #892, #894).
• Added tests for tzinfos input types. Patch by @​jbrockmendel (gh pr #891).

... (truncated)

Commits

• fc9b162 Merge pull request #974 from pganssle/release_2.8.1
• 4ccc8bb Update changelog for 2.8.1 release.
• 5fdbdbb Merge pull request #971 from pganssle/update_releasing
• e0f0b7e Add changelog for PR #971
• 9390c88 Update RELEASING documentation
• 3c9ccaa Change "Misc" to showcontent=True
• 58a4e46 Add "news" environment to tox
• 55301cd Fix Travis test for build command.
• e03f1de Add working build and release tox environments.
• 357c62c Merge pull request #973 from pganssle/strong_cache_race
• Additional commits viewable in compare view

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