Merge pull request #155 from timgraham/test-redis

Update test redis version to latest stable: 4.0.11

install_redis.sh

 #!/bin/bash
 
-: ${REDIS_VERSION:="2.6"}
+: ${REDIS_VERSION:="4.0.11"}
 
 test -d redis || git clone https://github.com/antirez/redis
 git -C redis checkout $REDIS_VERSION