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

src/documents/migrations/0002_auto_20151226_1316.py

@@ -1,6 +1,4 @@
-# -*- coding: utf-8 -*-
 # Generated by Django 1.9 on 2015-12-26 13:16
-from __future__ import unicode_literals
 
 from django.db import migrations, models
 import django.utils.timezone
@@ -21,7 +19,8 @@ class Migration(migrations.Migration):
             model_name="document",
             name="created",
             field=models.DateTimeField(
-                default=django.utils.timezone.now, editable=False
+                default=django.utils.timezone.now,
+                editable=False,
             ),
         ),
     ]