Upgrade django-pyscss to 1.0.3 for Horizon

The version we have now, 1.0.2, has a bug that prevents us from
unbundling the bootstrap 3 files with xstatic. This bug has just
been fixed upstream, and a new version, 1.0.3 is available with
the fix.

Change-Id: Ie70bd8ac0543e138b6a76c10732c7dc98ae63ce8
Closes-bug: 1369514
Merge "Upgrade django-pyscss to 1.0.3 for Horizon"