Fixed django.utils.simplejson deprecation warning

Fixed deprecation warning for django1.6 with try/except import json as simplejson

lib/python2.7/site-packages/zebra/views.py:5: DeprecationWarning: django.utils.simplejson is deprecated; use json instead.
  from django.utils import simplejson
Merge pull request #35 from iepathos/patch-1

Fixed django.utils.simplejson deprecation warning