x11/hs-xmobar: Fix WWW

xmobar.org currently seems to be an irrelevant site.

PR: 298929
Reported by: scottro (on forums.freebsd.org)
URL: https://forums.freebsd.org/threads/labwc-philosophy.103904/post-776856
Approved by: portmgr (blanket)
Approved by: osa, vvd (Mentors, implicit)
MFH: 2026Q3

(cherry picked from commit 9d573d0d52f877fbbdd6ffe74d3055dfe8c042dc)