Tweak documentation for AGI Hangup command.

(closes issue ASTERISK-17999)
Reported by: Ben Klang
Patches:
     hangup-doc.diff - uploaded by Ben Klang (License #5876)

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@323154 65c4cc65-6c06-0410-ace0-fbb531ad65f3

res/res_agi.c

@@ -297,7 +297,7 @@ ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
 	</agi>
 	<agi name="hangup" language="en_US">
 		<synopsis>
-			Hangup the current channel.
+			Hangup a channel.
 		</synopsis>
 		<syntax>
 			<parameter name="channelname" />