AMI: Bumping AMI non-breaking number for Asterisk 13.20.0 release

A few changes were made to AMI:

 * Fixed "(null):" header in AMI AsyncAGIEnd event
 * A mute header was added to the ConfbridgeJoin AMI event
 * ConfbridgeList action's ConfbridgeList events now output all
   the standard channel snapshot headers

Change-Id: I94a82a44b02c91becae08d254e9a56abba5697cf

include/asterisk/manager.h

@@ -54,7 +54,7 @@
 - \ref manager.c Main manager code file
  */
 
-#define AMI_VERSION                     "2.10.3"
+#define AMI_VERSION                     "2.10.4"
 #define DEFAULT_MANAGER_PORT 5038	/* Default port for Asterisk management via TCP */
 #define DEFAULT_MANAGER_TLS_PORT 5039	/* Default port for Asterisk management via TCP */