fixed jsonfield for django 1.5

openslides/utils/jsonfield/fields.py

@@ -1,8 +1,8 @@
+import json
+
 from django.db import models
 from django.core.serializers.json import DjangoJSONEncoder
-from django.utils import simplejson as json
 from django.utils.translation import ugettext_lazy as _
-
 from django.forms.fields import Field
 from django.forms.util import ValidationError as FormValidationError