cannot search chinese about doks

[HarborZeng]

I noticed that flexSearch may be updated, so the api has changed too.

We should define a decode function rather than return false as mentioned here https://github.com/nextapps-de/flexsearch#how-to-contribute and here https://getdoks.org/docs/reference-guides/flexsearch/#chinese-japanese-or-korean

    encode: function (str){
      return str.split("");
    },
    tokenize: function(str){
        return str.replace(/[\x00-\x7F]/g, "").split("");
    },

[h-enk]

See: #208