mediawiki: use a character literal

Change-Id: I1dadf4f905fcf06aee616cc0cfea3d77a145a3a1
Reviewed-on: https://gerrit.libreoffice.org/11371
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>