Remove 'vendor' dir reference that doesn't exist in tarball
Remove 'vendor' dir reference that doesn't exist in tarball

kennethjiang/heroku-buildpack-python-libffi,kennethjiang/heroku-buildpack-python-libffi,kennethjiang/heroku-buildpack-python-libffi,mfenniak/heroku-buildpack-python-libffi,mfenniak/heroku-buildpack-python-libffi,mfenniak/heroku-buildpack-python-libffi