build(deps): bump attrs from 19.3.0 to 20.1.0

Bumps [attrs](https://github.com/python-attrs/attrs) from 19.3.0 to 20.1.0.
- [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...20.1.0)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements.txt

@@ -18,4 +18,4 @@ tweepy==3.9.0
 venusian==3.0.0
 watchdog==0.10.3
 yarl==1.4.2
-attrs==19.3.0
+attrs==20.1.0