cffi missing in the requirements

[bors-ltd]

Hi,

I created a fresh (3.5) venv, and ran "pip install pygit2". It failed on importing cffi:

Collecting pygit2
  Downloading pygit2-0.23.2.tar.gz (464kB)
    100% |████████████████████████████████| 466kB 518kB/s
    Complete output from command python setup.py egg_info:
    Traceback (most recent call last):
      File "<string>", line 20, in <module>
      File "/private/var/folders/g6/66c3npm57lx6b2vp13nlsc4h0000gn/T/pip-build-ndy0njcn/pygit2/setup.py", line 58, in <module>
        from libgit2_build import __version__, get_libgit2_paths
      File "pygit2/libgit2_build.py", line 71, in <module>
        import cffi
    ImportError: No module named 'cffi'

    ----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /private/var/folders/g6/66c3npm57lx6b2vp13nlsc4h0000gn/T/pip-build-ndy0njcn/pygit2

Should it changed anything, this is a Mac platform, with Python installed via brew.

I've checked the other issues, but they talk about compiling issues or PyPy (?).

[jdavid]

Theoretically this should be fixed by 203335b ; in practice we will only know with the next release.
For now just "pip install cffi" first.

[cvrebert]

Similar: #380

[jdavid]

fixed with the new release