Fix the sample settings code for the template context processor.
Fix the sample settings code for the template context processor.

The fix is actually double:

- The function name was wrong (``account_status``, not ``expiration``)

- The code was intended as a tuple, but a single-element tuple needs a
  trailing comma, or it'll just be a string.

philippeowagner/django-plans,kevwilde/django-plans,andresriancho/django-plans,cypreess/django-plans,cypreess/django-plans,philippeowagner/django-plans