package/arp-scan: update upstream URL in Config.in help

Signed-off-by: Matt Weber <matthew.weber@rockwellcollins.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/arp-scan/Config.in

@@ -7,4 +7,4 @@ config BR2_PACKAGE_ARP_SCAN
 	  arp-scan is a command-line tool that uses the ARP protocol to
 	  discover and fingerprint IP hosts on the local network.
 
-	  http://www.nta-monitor.com/wiki/index.php/Arp-scan_Documentation
+	  https://github.com/royhills/arp-scan