OPER: Fix sent MODE string

irc/server.go

 		mode: Operator,
 		op:   Add,
 	}}
-	client.Send(nil, server.nameString, "MODE", client.nickString, client.nickString, modech.String())
+	client.Send(nil, server.nameString, "MODE", client.nickString, modech.String())
 	return false
 }