Fix CRC16 encode : string to bytes

It's related to https://github.com/xetorthio/jedis/commit/96c762b8806f153ec5e5d57d010d25c2ad90a94b#commitcomment-7903844

Conversion of String key in CRC16 should use SafeEncoder.encode() instead of String.getBytes().

@Fomky Could you please check it can support GBK?

Please review and comment!
Thanks!