x11/plasma-scriptengine-ruby: fix build

The commit r415864 (aka "Remove expired misc/kdehier4 and update
all of its consumers to not reference it any longer") for
x11/plasma-scriptengine-ruby dropped "kdelibs". This re-adds
kdelibs to USE_KDE4.

PR: 209835
Submitted by: Tobias C.Berner <tcberner@gmail.com> (kde)