build(deps): Bump pytz from 2019.3 to 2020.1 in /bot

Bumps [pytz](https://github.com/stub42/pytz) from 2019.3 to 2020.1.
- [Release notes](https://github.com/stub42/pytz/releases)
- [Commits](stub42/pytz@release_2019.3...release_2020.1)

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

Author: dependabot-preview[bot]

bot/requirements.txt

@@ -2,7 +2,7 @@
 google-cloud-storage==1.27.0
 libmozdata==0.1.68
 pytoml==0.1.21
-pytz==2019.3
+pytz==2020.1
 pyyaml==5.3.1
 tenacity==6.1.0
 zstandard==0.13.0