I think I fixed a tiny pip install bug

[Serbipunk]

With no cffi in requirements.txt, just starting markdown2pdf installation with pip install,

these error will arise, like

        replace_conflicting=replace_conflicting
      File "/usr/local/lib/python3.5/dist-packages/pkg_resources/__init__.py", line 1060, in best_match
        return self.obtain(req, installer)
      File "/usr/local/lib/python3.5/dist-packages/pkg_resources/__init__.py", line 1072, in obtain
        return installer(requirement)
      File "/usr/local/lib/python3.5/dist-packages/setuptools/dist.py", line 581, in fetch_build_egg
        return cmd.easy_install(req)
      File "/usr/local/lib/python3.5/dist-packages/setuptools/command/easy_install.py", line 670, in easy_install
        raise DistutilsError(msg)
    distutils.errors.DistutilsError: Could not find suitable distribution for Requirement.parse('cffi>=1.1.0')

    ----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /tmp/pip-install-f8j_a507/cairocffi/

merging it helps, I think ~