Django 1.8 fails with an ImproperlyConfigured exception when `fields` or
`exclude` isn't set:

```
class Meta:
 fields = '__all__'
```

on all descendents of ModelForm.

Omitting this is deprecated in 1.7:

https://docs.djangoproject.com/en/1.7/topics/forms/modelforms/#selecting-the-fields-to-use

Change-Id: I575ad045ffaf456606f78e269757153949a2344a
diff --git a/xos/admin.py b/xos/admin.py
index 464f197..80bc142 100644
--- a/xos/admin.py
+++ b/xos/admin.py
@@ -60,6 +60,7 @@
 
     class Meta:
         model = VTNService
+        fields = '__all__'
 
 class VTNServiceAdmin(ReadOnlyAwareAdmin):
     model = VTNService