Bug 28417: (follow-up) Fix typo

Bug 28417: (follow-up) Fix typo

- There are CAS demo servers, pick one [1]
- They all seem to have the same user/pass as of writing this:
  User: casuser
  Password: Mellon

To test:
1. Enable CAS and all related preferences. I chose v3 or higher, it only affects the logout action.
2. Set the CAS URL: https://casserver.herokuapp.com/cas (note that if you click on any of the examples, they include a trailing /login, don't put it).
3. Generate a Koha user, with userid: casuser (I also used that for cardnumber, just in case). Set no password to the user, or its irrelevant anyway. Add it stff permissions.
4. Open your Koha OPAC, I use KTD thus:
   http://kohadev.myDNSname.org:8080
5. Try to login using CAS
=> SUCCESS: You are redirected to the right login page
6. Login using casuser/Mellon as advertised in the 'demos' site.
=> SUCCESS: You are logged in!
7. Now logout
=> SUCCESS: You are sent to CAS so they know you wanted to logout (if you enabled CAS logout)
8. Repeat on the staff interface.
=> SUCCESS: Things work!
9. Apply this patches, restart all the things:
   $ restart_all
10. Repeat all in OPAC and admin interfaces
=> SUCCESS: Things work!
11. Sign off :-D

[1] https://apereo.github.io/cas/Demos.html

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>