build(deps): bump google-cloud-storage from 1.30.0 to 1.31.0 in /bot

Bumps [google-cloud-storage](https://github.com/googleapis/python-storage) from 1.30.0 to 1.31.0.
- [Release notes](https://github.com/googleapis/python-storage/releases)
- [Changelog](https://github.com/googleapis/python-storage/blob/master/CHANGELOG.md)
- [Commits](googleapis/python-storage@v1.30.0...v1.31.0)

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

Author: dependabot[bot]

bot/requirements.txt

@@ -1,5 +1,5 @@
 -e ../tools #egg=code-coverage-tools
-google-cloud-storage==1.30.0
+google-cloud-storage==1.31.0
 libmozdata==0.1.68
 pytoml==0.1.21
 pytz==2020.1