Correct documentation for ConfbridgeList AMI action

The documentation for ConfbridgeList states that the Conference field is
optional. That's not really the case: if you fail to provide a Conference
number, the command will kick back an error.

(closes issue AST-1090)
Reported by: John Bigelow
........

Merged revisions 380028 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@380029 65c4cc65-6c06-0410-ace0-fbb531ad65f3

apps/app_confbridge.c

@@ -161,7 +161,7 @@ ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
 		</synopsis>
 		<syntax>
 			<xi:include xpointer="xpointer(/docs/manager[@name='Login']/syntax/parameter[@name='ActionID'])" />
-			<parameter name="Conference" required="false">
+			<parameter name="Conference" required="true">
 				<para>Conference number.</para>
 			</parameter>
 		</syntax>