kamailio.cfg: updated the comment about kamailio version

etc/kamailio.cfg

@@ -1,6 +1,6 @@
 #!KAMAILIO
 #
-# Kamailio (OpenSER) SIP Server v4.0 - default configuration script
+# Kamailio (OpenSER) SIP Server v4.2 - default configuration script
 #     - web: http://www.kamailio.org
 #     - git: http://sip-router.org
 #