iOS 11.1 compatibility

[jcea]

Testing versión 0.3 from PYPI. iPhone 6, iOS 11.1

jcea@jcea:~$ python
Python 2.7.14 (default, Sep 20 2017, 16:03:25) 
[GCC 5.4.0 20160609] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from ptpy import PTPy
>>> camera = PTPy()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.7/site-packages/ptpy/__init__.py", line 135, in __new__
    instance._obtain_the_knowledge()
  File "/usr/local/lib/python2.7/site-packages/ptpy/ptp.py", line 863, in _obtain_the_knowledge
    self.__prop_desc[p] = self.get_device_prop_desc(p)
  File "/usr/local/lib/python2.7/site-packages/ptpy/ptp.py", line 1059, in get_device_prop_desc
    result = self._parse_if_data(response, self._DevicePropDesc)
  File "/usr/local/lib/python2.7/site-packages/ptpy/ptp.py", line 824, in _parse_if_data
    if hasattr(response, 'Data') else None)
  File "/usr/local/lib/python2.7/site-packages/construct/core.py", line 158, in parse
    return self.parse_stream(BytesIO(data), context, **kw)
  File "/usr/local/lib/python2.7/site-packages/construct/core.py", line 171, in parse_stream
    return self._parse(stream, context2, "(parsing)")
  File "/usr/local/lib/python2.7/site-packages/construct/core.py", line 867, in _parse
    subobj = sc._parse(stream, context, path)
  File "/usr/local/lib/python2.7/site-packages/construct/core.py", line 2788, in _parse
    raise e.__class__("%s\n    %s" % (e, path))
construct.core.FieldError: could not read enough bytes, expected 128, found 33
    (parsing) -> FactoryDefaultValue