Add missing document indexing migration to sort indexes by label.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

mayan/apps/document_indexing/migrations/0013_auto_20170714_2133.py

@@ -0,0 +1,19 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.10.7 on 2017-07-14 21:33
+from __future__ import unicode_literals
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('document_indexing', '0012_auto_20170530_0728'),
+    ]
+
+    operations = [
+        migrations.AlterModelOptions(
+            name='index',
+            options={'ordering': ('label',), 'verbose_name': 'Index', 'verbose_name_plural': 'Indexes'},
+        ),
+    ]