[telegram] Handle error when formatting formData
[telegram] Handle error when formatting formData

Bug:

  The method TelegramBot#_formatSendData() throws an error
  if the Buffer file type is NOT supported. We need to handle
  it, by returning a Promise that is reject with the originally
  thrown exception.

References:

  * PR trying to achieve the same: https://github.com/yagop/node-telegram-bot-api/pull/66

yagop/node-telegram-bot-api