Use a smoother running average for avg_ttl in INFO.
Use a smoother running average for avg_ttl in INFO.

Reported here:
https://www.reddit.com/r/redis/comments/42r0i0/avg_ttl_varies_a_lot/

louisliangjun/redis,maodeyi/redis_lua,louisliangjun/redis,splitice/redis,ramonsnir/redis,louisliangjun/redis,splitice/redis,ramonsnir/redis,louisliangjun/redis,splitice/redis,maodeyi/redis_lua,splitice/redis,maodeyi/redis_lua,ramonsnir/redis