release-v1.6.27-20200330

2020-03-25 Alibaba Cloud.

* VERSION: 1.6.27
* BUGFIX: transaction bug that only using one key but still raised "not
hashed in the same slot" error, see #257.
* IMPROVE: polish redis save rdb failed log, see #256.
* IMPROVE: support mset/msetnx command, see #247.
* IMPROVE: change "rewrite" to "key_exists" in configuration, see #259.