Restore gnome-shell-sass submodule

Commit 68f439425bd accidentally dropped the changes from the last
couple of months ...

diff --git a/data/theme/gnome-shell-sass b/data/theme/gnome-shell-sass
index 6ccc1808114d803f6699877143c614f14aaf14ea..b2190083c256564258fce97645ae6da72e9d0f7f 160000 (submodule)
--- a/data/theme/gnome-shell-sass
+++ b/data/theme/gnome-shell-sass
@@ -1 +1 @@
-Subproject commit 6ccc1808114d803f6699877143c614f14aaf14ea
+Subproject commit b2190083c256564258fce97645ae6da72e9d0f7f