Bump attrs from 19.3.0 to 20.2.0

Bumps [attrs](https://github.com/python-attrs/attrs) from 19.3.0 to 20.2.0.
- [Release notes](https://github.com/python-attrs/attrs/releases)
- [Changelog](https://github.com/python-attrs/attrs/blob/master/CHANGELOG.rst)
- [Commits](python-attrs/attrs@19.3.0...20.2.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Author: dependabot-preview[bot]

requirements.txt

@@ -1,6 +1,6 @@
 aiohttp==3.6.2
 async-timeout==3.0.1
-attrs==19.3.0
+attrs==20.2.0
 beautifulsoup4==4.9.1
 bs4==0.0.1
 certifi==2019.11.28