In zbxgt.sh script parameter to send to chat should be "zbxtg;chat" but not a "zbxtg;channel"

From a script code:

```
TG_CHAT=0 # send message to chat or to private chat to user
METHOD="txt" # sendMessage (simple text) or sendPhoto (attached image)

echo "${BODY}" | grep -q "${ZBX_TG_PREFIX};graphs" && METHOD="image"
echo "${BODY}" | grep -q "${ZBX_TG_PREFIX};chat" && TG_CHAT=1
echo "${BODY}" | grep -q "${ZBX_TG_PREFIX};debug" && ISDEBUG="TRUE" 
```
