Bump redis from 3.3.8 to 3.5.3 (#745)

Bumps [redis](https://github.com/andymccurdy/redis-py) from 3.3.8 to 3.5.3.
- [Release notes](https://github.com/andymccurdy/redis-py/releases)
- [Changelog](https://github.com/andymccurdy/redis-py/blob/master/CHANGES)
- [Commits](redis/redis-py@3.3.8...3.5.3)

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

requirements_dev_optional.txt

@@ -7,7 +7,7 @@ ipytree==0.2.1
 # don't let pyup change pinning for azure-storage-blob, need to pin to older
 # version to get compatibility with azure storage emulator on appveyor (FIXME)
 azure-storage-blob==2.0.1 # pyup: ignore
-redis==3.3.8
+redis==3.5.3
 pymongo==3.11.4
 # optional test requirements
 tox==3.14.0