Fix migration numbering

awx/main/migrations/0028_v330_add_tower_verify.py

@@ -0,0 +1,18 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+# AWX
+from awx.main.migrations import _credentialtypes as credentialtypes
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('main', '0027_v330_emitted_events'),
+    ]
+
+    operations = [
+        migrations.RunPython(credentialtypes.add_tower_verify_field),
+    ]