nixos/znc: Fix URL XML for config option

(cherry picked from commit b8dc0f9)

nixos/modules/services/networking/znc/default.nix

@@ -151,7 +151,7 @@ in
         '';
         description = ''
           Configuration for ZNC, see
-          <literal>https://wiki.znc.in/Configuration</literal> for details. The
+          <link xlink:href="https://wiki.znc.in/Configuration"/> for details. The
           Nix value declared here will be translated directly to the xml-like
           format ZNC expects. This is much more flexible than the legacy options
           under <option>services.znc.confOptions.*</option>, but also can't do