Unsupported keyword argument 'score_cast_func' to zrangebyscore()

In the latest version of `redis-py`, [zrangebyscore() accepts a keyword argument called score_cast_func.](http://redis-py.readthedocs.io/en/latest/#redis.StrictRedis.zrangebyscore)

Fakeredis [does not support it yet](https://github.com/jamesls/fakeredis/blob/master/fakeredis.py#L1630-L1631).

I'll do a PR ASAP.