Bug 18830: Fix phrasing of screen message

Bug 18830: Fix phrasing of screen message

Verb should be plural in this message

Signed-off-by: Israelex A Veleña for KohaCon17 <israelex19@gmail.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit 8a0ecda6c4ff368b9ff7a18593d7bdf4fc07e541)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
(cherry picked from commit 5bbb863147959471a1a11e019eb18007c5c78583)
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>