Bump pylint from 1.8.4 to 2.7.3 (#151)

Bumps [pylint](https://github.com/PyCQA/pylint) from 1.8.4 to 2.7.3.
- [Release notes](https://github.com/PyCQA/pylint/releases)
- [Changelog](https://github.com/PyCQA/pylint/blob/master/ChangeLog)
- [Commits](pylint-dev/pylint@pylint-1.8.4...pylint-2.7.3)

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

Author: dependabot-preview[bot]

requirements.txt

@@ -22,7 +22,7 @@ mock==2.0.0
 pbr==4.0.2
 pycodestyle==2.4.0
 Pygments==2.2.0
-pylint==1.8.4
+pylint==2.7.3
 pytest-runner==4.2
 python-dateutil==2.6.1
 PyYAML==5.1