message: Use BytesIO instead of StringIO for python2/3 compatibility
diff: @@ -12,13 +12,9 @@ try:
  except ImportError:
  import pickle
  +import io
  import logging
  -try:
  - import StringIO
  -except ImportError:
  - import io as StringIO
  -
  import boto3
  from werkzeug.contrib.cache import BaseCache
  @@ -56,7 +52,7 @@ class S3Cache(BaseCache):
  if not self._key_exists(key):
  return None
  else:
  - value_file = StringIO.StringIO()
  + value_file = io.BytesIO()
  try:
  self.s3_client.download_fileobj(
  @@ -117,7 +113,7 @@ class S3Cache(BaseCache):
  ``pickle.PickleError``.
  :rtype: boolean
  """
  - value_file = StringIO.StringIO()
  + value_file = io.BytesIO()
  pickle.dump(value, value_file)
  try:
  