Add setuptools_scm to deps to forestall egging
Add setuptools_scm to deps to forestall egging

If setuptools_scm is installed in the virtualenv where Tox runs (where
it builds the sdist) *and* is installed as a dep before the package is
installed (pip then builds from the sdist, IIUC), then Tox can be run
off-line and setuptools/easy_install will not download the egg.

wcooley/python-gryaml