Update pkgs/servers/monitoring/kapacitor/default.nix

Remove platforms meta attribute as this is automatically set for GoModules.

pkgs/servers/monitoring/kapacitor/default.nix

···
     license = licenses.mit;
     changelog = "https://github.com/influxdata/kapacitor/blob/master/CHANGELOG.md";
     maintainers = with maintainers; [ offline totoroot ];
-    platforms = with platforms; linux;
   };
 }