build(deps): Bump structlog from 19.2.0 to 20.1.0 in /tools (#403)

Bumps [structlog](https://github.com/hynek/structlog) from 19.2.0 to 20.1.0.
- [Release notes](https://github.com/hynek/structlog/releases)
- [Changelog](https://github.com/hynek/structlog/blob/master/CHANGELOG.rst)
- [Commits](hynek/structlog@19.2.0...20.1.0)

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

Author: dependabot-preview[bot]

tools/requirements.txt

@@ -2,5 +2,5 @@ aiohttp==3.6.2
 async-timeout==3.0.1
 logbook==1.5.3
 raven==6.10.0
-structlog==19.2.0
+structlog==20.1.0
 taskcluster==24.2.0