trivial: fix missing migration

chrono/agendas/migrations/0008_auto_20160910_1319.py

@@ -1,6 +1,7 @@
 # -*- coding: utf-8 -*-
 from __future__ import unicode_literals
 
+import django
 from django.db import migrations, models
 
 
@@ -19,7 +20,14 @@ class Migration(migrations.Migration):
                     models.AutoField(verbose_name='ID', serialize=False, auto_created=True, primary_key=True),
                 ),
                 ('label', models.CharField(max_length=100, verbose_name='Label')),
-                ('duration', models.IntegerField(default=30, verbose_name='Duration (in minutes)')),
+                (
+                    'duration',
+                    models.IntegerField(
+                        default=30,
+                        validators=[django.core.validators.MinValueValidator(1)],
+                        verbose_name='Duration (in minutes)',
+                    ),
+                ),
             ],
             options={'ordering': ['label'],},
         ),