Bump redis from 2.10.6 to 3.5.3

Bumps [redis](https://github.com/andymccurdy/redis-py) from 2.10.6 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@2.10.6...3.5.3) Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Author: dependabot-preview[bot]

requirements.txt

@@ -1,3 +1,3 @@
 Faker==0.8.6
 Flask==1.0
-redis==2.10.6
+redis==3.5.3