kamailio.cfg: set version to 3.4 in the top comments

etc/kamailio.cfg

@@ -1,6 +1,6 @@
 #!KAMAILIO
 #
-# Kamailio (OpenSER) SIP Server v3.3 - default configuration script
+# Kamailio (OpenSER) SIP Server v3.4 - default configuration script
 #     - web: http://www.kamailio.org
 #     - git: http://sip-router.org
 #