Downgrade minimum required Python version

[h6197627]

According to this tool waybackpy is still fully compatible with Python 3.6. I understand that there is no point to stick to old versions, but considering that current code does not require any changes, there is also no point to cut off some users without real need. It will be good for folks who are still sitting with Ubuntu 18.04 :)

[akamhy]

sounds reasonable to me, what about you @eggplants?

[eggplants]

LGTM, and thank you @h6197627.

[akamhy]

@h6197627 checkout https://github.com/akamhy/waybackpy/releases/tag/3.0.5 or https://pypi.org/project/waybackpy/3.0.5/

[h6197627]

Thanks, @akamhy!