build(deps): Bump pyyaml from 5.3 to 5.3.1 in /bot (#473)

Bumps [pyyaml](https://github.com/yaml/pyyaml) from 5.3 to 5.3.1.
- [Release notes](https://github.com/yaml/pyyaml/releases)
- [Changelog](https://github.com/yaml/pyyaml/blob/master/CHANGES)
- [Commits](yaml/pyyaml@5.3...5.3.1)

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

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

Author: dependabot-preview[bot]

bot/requirements.txt

@@ -3,6 +3,6 @@ google-cloud-storage==1.26.0
 libmozdata==0.1.65
 pytoml==0.1.21
 pytz==2019.3
-pyyaml==5.3
+pyyaml==5.3.1
 tenacity==6.1.0
 zstandard==0.13.0