Update hangup_rx.lua

Working on replacing this php command for sending the email. It appears this is locking freeswitch and not completing.

Reverting this commit.
- 63e1f7741e

app/scripts/resources/scripts/app/fax/resources/scripts/hangup_rx.lua

@@ -225,9 +225,7 @@
 		cmd = cmd .. "fax_prefix=false ";
 	end
 	freeswitch.consoleLog("notice", "[fax] command: " .. cmd .. "\n");
-	local handle = io.popen(cmd);
-	result = handle:read("*a");
-	handle:close();
+	result = api:execute("system", cmd);
 
 --add to fax logs
 	sql = "insert into v_fax_logs ";