Update asyncpg to 0.20.1

[pyup-bot]

This PR updates asyncpg from 0.19.0 to 0.20.1.

Changelog

0.20.0

Improvements

* Support Python 3.8
(by 1st1 in 504)

* Support PgBouncer by sending only a single SYNC message per query 
(by fvannee in b043fbd3)

Bug Fixes

* Handle IP values with prefix in "inet" type as `ipaddress.IPvXInterface`
(by elprans in 5a4daf71 for 497)

* Close transport if connection times out
(by hexrain in 926f4833 for 468)

* Use faster UUID codecs; make UUID decoding/encoding/operations 2-7x faster
(by 1st1 in edde3ff4)

* Use `loop.start_tls()` to upgrade connections to SSL
(by 1st1 in bdba7ce7)

Build

* Bump Cython to 0.29.14
(by 1st1 in 7cb31bc6)

Links

• PyPI: https://pypi.org/project/asyncpg
• Changelog: https://pyup.io/changelogs/asyncpg/
• Repo: https://github.com/MagicStack/asyncpg

[pyup-bot]

Closing this in favor of #58