Log Message:
py-limits: updated to 1.5.1

1.5.1:
* Bug fix
  * Remove duplicate call to ttl in RedisStorage
  * Initialize master/slave connections for RedisSentinel once

1.5:
* Bug fix for handling TTL response from Redis when key doesn’t exist
* Support Memcache over unix domain socket
* Support Memcache cluster
* Pass through constructor keyword arguments to underlying storage
  constructor(s)
* CI & test improvements