Add "FNC" (forced nick changes) to ISUPPORT(005) numeric

Most probably this doesn't make any difference to any client, but it
seems correct. See <http://www.irc.org/tech_docs/005.html> for details.

src/ngircd/messages.h

@@ -1,6 +1,6 @@
 /*
  * ngIRCd -- The Next Generation IRC Daemon
- * Copyright (c)2001-2014 Alexander Barton (alex@barton.de) and Contributors.
+ * Copyright (c)2001-2020 Alexander Barton (alex@barton.de) and Contributors.
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -23,7 +23,7 @@
 #define RPL_MYINFO_MSG			"004 %s %s ngircd-%s %s %s"
 #define RPL_ISUPPORTNET_MSG		"005 %s NETWORK=%s :is my network name"
 #define RPL_ISUPPORT1_MSG		"005 %s RFC2812 IRCD=ngIRCd CHARSET=UTF-8 CASEMAPPING=ascii PREFIX=(qaohv)~&@%%+ CHANTYPES=%s CHANMODES=beI,k,l,imMnOPQRstVz CHANLIMIT=%s:%d :are supported on this server"
-#define RPL_ISUPPORT2_MSG		"005 %s CHANNELLEN=%d NICKLEN=%d TOPICLEN=%d AWAYLEN=%d KICKLEN=%d MODES=%d MAXLIST=beI:%d EXCEPTS=e INVEX=I PENALTY :are supported on this server"
+#define RPL_ISUPPORT2_MSG		"005 %s CHANNELLEN=%d NICKLEN=%d TOPICLEN=%d AWAYLEN=%d KICKLEN=%d MODES=%d MAXLIST=beI:%d EXCEPTS=e INVEX=I PENALTY FNC :are supported on this server"
 
 #define RPL_TRACELINK_MSG		"200 %s Link %s-%s %s %s V%s %ld %d %d"
 #define RPL_TRACEOPERATOR_MSG		"204 %s Oper 2 :%s"