Fix pyScss version in lower-constraints.txt
Fix pyScss version in lower-constraints.txt

Horizon requires  pyScss>=1.3.7 [1] but lower-constraints.txt
in sahara-dashboard uses pyScss 1.3.4 which can cause the
failure in future. So this patch update pyScss version in
lower-constraints.txt to sync the change.

[1] https://review.opendev.org/#/c/715241/

Change-Id: Ia2415a21f643648ebd02644224ec44dcc773713a

openstack/sahara-dashboard,openstack/sahara-dashboard,openstack/sahara-dashboard,openstack/sahara-dashboard