Bump astroid from 2.3.3 to 2.4.2 (#12)

Bumps [astroid](https://github.com/PyCQA/astroid) from 2.3.3 to 2.4.2.
- [Release notes](https://github.com/PyCQA/astroid/releases)
- [Changelog](https://github.com/PyCQA/astroid/blob/master/ChangeLog)
- [Commits](https://github.com/PyCQA/astroid/compare/astroid-2.3.3...astroid-2.4.2)

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Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

requirements.txt

@@ -1,5 +1,5 @@
 aiohttp==3.6.2
-astroid==2.3.3
+astroid==2.4.2
 async-timeout==3.0.1
 attrs==19.3.0
 autopep8==1.5