Reference: https://medium.com/@hatsukiotowa/%E6%89%8B%E6%8A%8A%E6%89%8B%E6%95%99%E4%BD%A0%E6%90%AD%E5%BB%BA%E8%81%8A%E5%A4%A9%E6%A9%9F%E5%99%A8%E4%BA%BA-linebot-python-qnamaker-heroku-01%E5%BB%BA%E9%80%A0qnamaker-99b88e8993b4 https://github.com/ninanina74/lot-homework-sourcecode/blob/master/app.py