add the method of deleting keys by regular express

[kyohaifeng]

添加方法deleteRegKeys(),利用scan和pipeline删除符合正则表达式条件的KEY的值 by Kyohaifeng

[coveralls]

Coverage decreased (-6.0%) to 94.0% when pulling 272d244 on kyohaifeng:think-redis-delKeys into de6bcc5 on thinkjs:master.

[lizheming]

think-redis@1.1.2 已发布，感谢 PR。