bugfix: rename default img name

rename default img

djangoldp_polls/migrations/0009_auto_20200911_1316.py

+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.29 on 2020-09-11 13:16
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('djangoldp_polls', '0008_auto_20200820_1103'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='poll',
+            name='image',
+            field=models.URLField(default='http://localhost:8000/media/defaultpoll.png', verbose_name='Illustration'),
+        ),
+    ]