Changed tuple choices to list in docs.

docs/topics/forms/modelforms.txt

@@ -165,11 +165,11 @@ Consider this set of models::
     from django.db import models
     from django.forms import ModelForm
 
-    TITLE_CHOICES = (
+    TITLE_CHOICES = [
         ('MR', 'Mr.'),
         ('MRS', 'Mrs.'),
         ('MS', 'Ms.'),
-    )
+    ]
 
     class Author(models.Model):
         name = models.CharField(max_length=100)