Fix Dockerfile (cache clear of apt)
Fix Dockerfile (cache clear of apt)

redis/redis-py,alisaifee/redis-py,alisaifee/redis-py,mozillazg/redis-py-doc,andymccurdy/redis-py,andymccurdy/redis-py,andymccurdy/redis-py,mozillazg/redis-py-doc,redis/redis-py