Bug 20854: (QA follow-up) Rephrase of the new casServerVersion pref description

Bug 20854: (QA follow-up) Rephrase of the new casServerVersion pref description

For another related change, see:
https://en.wikipedia.org/wiki/Central_Authentication_Service

CAS = Central Authentication Service

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit 6aa6f115bd2330342675781400199a2f3152abf1)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
(cherry picked from commit a54e729319ea03baae1b8e65f409a8916ff77ba8)

Signed-off-by: Andrew Fuerste-Henry <andrew@bywatersolutions.com>