Use direct translation only on private chats

Otherwise it would reply to every single message on e.g. group chats.

@@ -34,10 +34,12 @@ bot.onText(/\/echo (.+)/, (msg, match) => {
 // Listen for any kind of message. Translate if it's not a command.
 bot.on('message', (msg) => {
   const chatId = msg.chat.id;
+  const chatType = msg.chat.type;
   const received_msg = msg.text;
 
-  // Ignore if input is a command
-  if (received_msg[0] == '/') {
+  // Ignore if input is a command or we are not on a private chat,
+  // since direct translation is to be used only on private chats.
+  if (received_msg[0] == '/' || chatType != 'private') {
     return;
   }