otherwise we will fail to install the build dependencies of
`lazy-object-proxy` from the wheelhouse. as `lazy-object-proxy` does not
add `setuptools_scm` in its `setup.py`, instead it lists
`setuptools_scm` in `setup.cfg` and `pyproject.toml` as a `build-system`
requires. but unfortunately, `pip download` only downloads the
install/run-time dependencies at this moment. and `lazy-object-proxy`
does not offer binary package for at least python2.7.
ideally, `pip download` should collects its dependencies like