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](https://github.com/python-attrs/attrs/compare/19.3.0...20.1.0)

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

requirements-indirect.txt

@@ -1,6 +1,6 @@
 altgraph==0.17
 appdirs==1.4.4
-attrs==19.3.0
+attrs==20.1.0
 bcrypt==3.1.7
 cffi==1.14.1
 cryptography==3.0