Updated pylint to 1.8.4

Summary:
Updated pylint to the latest version 1.8.4.
Change log available here.

Test Plan:
Installed in a virtual machine with the updated version of python-astroid and ran with Python files with/without errors.
All tests ran as expected.

Reviewers: Triage Team, DataDrake

Reviewed By: Triage Team, DataDrake

Subscribers: DataDrake, kyrios123

Differential Revision: https://dev.solus-project.com/D2884