Bug 34706: Fix capitalization - Cas to CAS

Bug 34706: Fix capitalization - Cas to CAS

CAS is an abbreviation and should use capital letters.

Test plan:
1. Enable the casAuthentication system preference.
2. Logout and view the login form.
3. Note that it says "Cas login".
4. Apply the patch.
5. Refresh the login page.
6. Note that it now says "CAS login".
7. Sign off.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Sam Lau <samalau@gmail.com>
Signed-off-by: Emily Lamancusa <emily.lamancusa@montgomerycountymd.gov>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>