Bump redis from 3.5.2 to 3.5.3

Bumps [redis](https://github.com/andymccurdy/redis-py) from 3.5.2 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@3.5.2...3.5.3)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Author: dependabot-preview[bot]

requirements.txt

@@ -1,7 +1,7 @@
 # Depending on what engine type you want to use
 # you will need one of the following
 #mysqlclient==1.4.6
-redis==3.5.2
+redis==3.5.3
 # python-gdbm # not available via pip
 
 # If you want to use gevent you will also require