[Pylint] Bump pylint version to latest

Older releases of pylint use  an internal API of
the astroid library that causes pylint
exceptions when parsing modules. The errors
are like:

 internal error with sending report for module ['manila/network/neutron/neutron_network_plugin.py']
 'Import' object has no attribute 'infer_name_module'

So let's use the latest version available
that doesn't have this issue.

[1] https://github.com/PyCQA/astroid/issues/649

Change-Id: I6031111e5c72470313642307b4596806cd5408df

tox.ini

@@ -106,7 +106,7 @@ commands =
 basepython = python3
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
-       pylint==2.1.1
+       pylint==2.3.1
 whitelist_externals = bash
 commands = bash ./tools/coding-checks.sh --pylint {posargs}