Handle Telegram API response in case of failure

[Marco Rougeth]

Bottery ignores errors from Telegram API. If, for example, an invalid token is used, no message is shown and, the process breaks because it tries to continue even if something is wrong with Telegram.

Traceback (most recent call last):
  File "bottery/telegram/engine.py", line 95, in polling
    tasks = [self.message_handler(msg) for msg in updates['result']]
KeyError: 'result'