Pylint issues arise on python 3.5.3

Summary

./setup.py test --adopts '-m pylint' passes on python 3.7 but fails on python 3.5.3.

Note: The following command also has the same effect and runs faster.

pylint --rcfile .pylintrc buildstream/

Steps to reproduce

Python 3.5.3

./setup.py test --adopts '-m pylint'

What is the current bug behavior?

The lint run passes on 3.7 but not 3.5.3.

What is the expected correct behavior?

Master should pass lint checks on all supported versions of python.

Relevant logs and/or screenshots

https://paste.gnome.org/ptaewygoy

https://asciinema.org/a/BfHy4QYsrzDVTluIAvfZyX1LP

Possible fixes

Other relevant information

• BuildStream version affected: master @ 56f2b2e4

---

/label ~bug