community/py3-dotenv: upgrade to 0.20.0

https://github.com/theskumar/python-dotenv/releases/tag/v0.20.0

Added

• Add encoding (Optional[str]) parameter to get_key, set_key and unset_key. (#379 by @bbc2)

Fixed

• Use dict to specify the entry_points parameter of setuptools.setup (#376 by @mgorny).
• Don't build universal wheels (#387 by @bbc2).