Update astroid to 2.5.6

[pyup-bot]

This PR updates astroid from 2.5.3 to 2.5.6.

Changelog

2.5.6

============================
Release Date: 2021-04-25

* Fix retro-compatibility issues with old version of pylint
Closes PyCQA/pylint4402

2.5.5

============================
Release Date: 2021-04-24

* Fixes the discord link in the project urls of the package.
Closes PyCQA/pylint4393

2.5.4

============================
Release Date: 2021-04-24

* The packaging is now done via setuptools exclusively. ``doc``, ``tests``, and ``Changelog`` are
not packaged anymore - reducing the size of the package greatly.

* Debian packaging is now  (officially) done in https://salsa.debian.org/python-team/packages/astroid.

* ``__pkginfo__`` now  only contain ``__version__`` (also accessible with ``astroid.__version__``),
other meta-information are still accessible with ``import importlib;metadata.metadata('astroid')``.

* Added inference tip for ``typing.Tuple`` alias

* Fix crash when evaluating ``typing.NamedTuple``

Closes PyCQA/pylint4383

* COPYING was removed in favor of COPYING.LESSER and the latter was renamed to LICENSE to make more apparent
that the code is licensed under LGPLv2 or later.

* Moved from appveyor and travis to Github Actions for continuous integration.

Links

• PyPI: https://pypi.org/project/astroid
• Changelog: https://pyup.io/changelogs/astroid/
• Repo: https://github.com/PyCQA/astroid

[codecov]

Codecov Report

Merging #70 (28c5143) into master (77f684a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #70   +/-   ##
=======================================
  Coverage   67.85%   67.85%           
=======================================
  Files           2        2           
  Lines          56       56           
=======================================
  Hits           38       38           
  Misses         18       18           

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[aragilar]

bors r+

[bors]

Build succeeded:

• aragilar.stringtopy
• codecov/patch
• codecov/project