app_queue: Fix documentation for QUEUE_MEMBER function.

It was a copy/paste of the QUEUE_MEMBER_COUNT function's synopsis.

ASTERISK-20986 #close
Reported by: Olivier Krief

Change-Id: If51ec481feb35824a4e78ab5600b197b819b10be

apps/app_queue.c

@@ -539,7 +539,8 @@ ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
 	</function>
 	<function name="QUEUE_MEMBER" language="en_US">
 		<synopsis>
-			Count number of members answering a queue.
+			Provides a count of queue members based on the provided criteria, or updates a
+			queue member's settings.
 		</synopsis>
 		<syntax>
 			<parameter name="queuename" required="false" />