Fix TypeError raised in logging (validate_models)

celery/fixups/django.py

@@ -1,10 +1,14 @@
 from __future__ import absolute_import
 
-import io
 import os
 import sys
 import warnings
 
+if sys.version_info[0] < 3 and not hasattr(sys, 'pypy_version_info'):
+    from StringIO import StringIO
+else:
+    from io import StringIO
+
 from kombu.utils import cached_property, symbol_by_name
 
 from datetime import datetime
@@ -152,7 +156,7 @@ class DjangoWorkerFixup(object):
             pass
         else:
             django_setup()
-        s = io.StringIO()
+        s = StringIO()
         try:
             from django.core.management.validation import get_validation_errors
         except ImportError: