Use BytesIO for raw data processing

Signed-off-by: Michal Čihař <michal@cihar.com>

weblate/trans/formats.py

@@ -23,6 +23,7 @@ File format specific behavior.
 
 from __future__ import unicode_literals
 
+from io import BytesIO
 import subprocess
 import os.path
 import re
@@ -33,7 +34,6 @@ import importlib
 from django.utils.translation import ugettext_lazy as _
 
 import six
-from six import StringIO
 
 from translate.convert import po2php
 from translate.storage.lisa import LISAfile
@@ -62,13 +62,12 @@ class ParseError(Exception):
     """Generic error for parsing."""
 
 
-class StringIOMode(StringIO):
+class StringIOMode(BytesIO):
     """
     StringIO with mode attribute to make ttkit happy.
     """
     def __init__(self, filename, data):
-        # pylint: disable=W0233
-        StringIO.__init__(self, data)
+        super(StringIOMode, self).__init__(self, data)
         self.mode = 'r'
         self.name = filename