Configures ruff as the one stop linter and resolves warnings it raised

src/documents/migrations/0019_add_consumer_user.py

@@ -1,6 +1,4 @@
-# -*- coding: utf-8 -*-
 # Generated by Django 1.10.5 on 2017-07-15 17:12
-from __future__ import unicode_literals
 
 from django.contrib.auth.models import User
 from django.db import migrations