Fixed Python 2.6 issue

polymorphic/formsets/models.py

@@ -1,4 +1,3 @@
-from collections import OrderedDict
 
 import django
 from django import forms
@@ -8,6 +7,11 @@ from django.forms.models import ModelForm, BaseModelFormSet, BaseInlineFormSet,
 from django.utils.functional import cached_property
 from .utils import add_media
 
+try:
+    from collections import OrderedDict
+except ImportError:
+    from django.utils.datastructures import SortedDict as OrderedDict  # Python 2.6
+
 
 class PolymorphicFormSetChild(object):
     """