Add forgotten (no-op) migration

Barely changes the help_text, this migration has no actual effect.

coin/billing/migrations/0004_auto_20161230_1803.py

@@ -0,0 +1,21 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import models, migrations
+import datetime
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('billing', '0003_auto_20150221_2226'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='invoice',
+            name='date',
+            field=models.DateField(default=datetime.date.today, help_text='Cette date sera d\xe9finie \xe0 la date de validation dans la facture finale', null=True, verbose_name='date'),
+            preserve_default=True,
+        ),
+    ]