107: Update cffi to 1.11.1 r=mithrandi


There's a new version of [cffi](https://pypi.python.org/pypi/cffi) available.
You are currently using **1.10.0**. I have updated it to **1.11.1**



These links might come in handy:  <a href="https://pypi.python.org/pypi/cffi">PyPI</a> | <a href="https://pyup.io/changelogs/cffi/">Changelog</a> | <a href="http://cffi.readthedocs.org">Docs</a> 



### Changelog
> 
>### 1.11.1

>=======

>* Fix tests, remove deprecated C API usage

>* Fix (hack) for 3.6.0/3.6.1/3.6.2 giving incompatible binary extensions
>  (cpython issue `29943`_)

>* Fix for 3.7.0a1+

>.. _`29943`: https://bugs.python.org/issue29943




>### 1.11

>=====

>* Support the modern standard types ``char16_t`` and ``char32_t``.
>  These work like ``wchar_t``: they represent one unicode character, or
>  when used as ``charN_t *`` or ``charN_t[]`` they represent a unicode
>  string.  The difference with ``wchar_t`` is that they have a known,
>  fixed size.  They should work at all places that used to work with
>  ``wchar_t`` (please report an issue if I missed something).  Note
>  that with ``set_source()``, you need to make sure that these types are
>  actually defined by the C source you provide (if used in ``cdef()``).

>* Support the C99 types ``float _Complex`` and ``double _Complex``.
>  Note that libffi doesn&#39;t support them, which means that in the ABI
>  mode you still cannot call C functions that take complex numbers
>  directly as arguments or return type.

>* Fixed a rare race condition when creating multiple ``FFI`` instances
>  from multiple threads.  (Note that you aren&#39;t meant to create many
>  ``FFI`` instances: in inline mode, you should write ``ffi =
>  cffi.FFI()`` at module level just after ``import cffi``; and in
>  out-of-line mode you don&#39;t instantiate ``FFI`` explicitly at all.)

>* Windows: using callbacks can be messy because the CFFI internal error
>  messages show up to stderr---but stderr goes nowhere in many
>  applications.  This makes it particularly hard to get started with the
>  embedding mode.  (Once you get started, you can at least use
>  ``ffi.def_extern(onerror=...)`` and send the error logs where it
>  makes sense for your application, or record them in log files, and so
>  on.)  So what is new in CFFI is that now, on Windows CFFI will try to
>  open a non-modal MessageBox (in addition to sending raw messages to
>  stderr).  The MessageBox is only visible if the process stays alive:
>  typically, console applications that crash close immediately, but that
>  is also the situation where stderr should be visible anyway.

>* Progress on support for `callbacks in NetBSD`__.

>* Functions returning booleans would in some case still return 0 or 1
>  instead of False or True.  Fixed.

>* `ffi.gc()`__ now takes an optional third parameter, which gives an
>  estimate of the size (in bytes) of the object.  So far, this is only
>  used by PyPy, to make the next GC occur more quickly (`issue 320`__).
>  In the future, this might have an effect on CPython too (provided
>  the CPython `issue 31105`__ is addressed).

>* Add a note to the documentation: the ABI mode gives function objects
>  that are *slower* to call than the API mode does.  For some reason it
>  is often thought to be faster.  It is not!

>.. __: https://bitbucket.org/cffi/cffi/issues/321/cffi-191-segmentation-fault-during-self
>.. __: ref.htmlffi-gc
>.. __: https://bitbucket.org/cffi/cffi/issues/320/improve-memory_pressure-management
>.. __: http://bugs.python.org/issue31105




>### 1.10.1

>=======







*Got merge conflicts? Close this PR and delete the branch. I'll create a new PR for you.*

Happy merging! 🤖