nixos/prometheus-dnsmasq-exporter: use a working default leasesPath

dnsmasq dhcp-leasefile defaults to /var/lib/dnsmasq/dnsmasq.leases, so
use that as the default for the exporter too. Curiously, the example was
using the working path, so this patch simply swaps "example" and
"default" values.

nixos/modules/services/monitoring/prometheus/exporters/dnsmasq.nix

@@ -21,8 +21,8 @@ in
     };
     leasesPath = mkOption {
       type = types.path;
-      default = "/var/lib/misc/dnsmasq.leases";
-      example = "/var/lib/dnsmasq/dnsmasq.leases";
+      default = "/var/lib/dnsmasq/dnsmasq.leases";
+      example = "/var/lib/misc/dnsmasq.leases";
       description = ''
         Path to the `dnsmasq.leases` file.
       '';