Merge #70

70: Update astroid to 2.5.6 r=aragilar a=pyup-bot


This PR updates [astroid](https://pypi.org/project/astroid) from **2.5.3** to **2.5.6**.



<details>
  <summary>Changelog</summary>
  
  
   ### 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(&#39;astroid&#39;)``.

* 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.
   ```
   
  
</details>


 

<details>
  <summary>Links</summary>
  
  - PyPI: https://pypi.org/project/astroid
  - Changelog: https://pyup.io/changelogs/astroid/
  - Repo: https://github.com/PyCQA/astroid
</details>



Co-authored-by: pyup-bot <github-bot@pyup.io>

pylint-requirements.txt

@@ -1,2 +1,2 @@
-astroid==2.5.3
+astroid==2.5.6
 pylint==2.7.2