Replaced six.BytesIO with io.BytesIO

tests/servers/test_basehttp.py

@@ -1,9 +1,10 @@
+from io import BytesIO
+
 from django.core.handlers.wsgi import WSGIRequest
 from django.core.servers.basehttp import WSGIRequestHandler
 from django.test import SimpleTestCase
 from django.test.client import RequestFactory
 from django.test.utils import captured_stderr
-from django.utils.six import BytesIO
 
 
 class Stub(object):