fix Japanese SEARCH_PLACEHOLDER

[k-harada413]

Hi,

I found Mistranslation in japanese.

• gitbook-plugin-theme-rangle-io_i18n\ja.json
  "SEARCH_PLACEHOLDER": "検索すると入力"

You should fix to 入力すると検索.

thank you.

[k-harada413]

sorry.
this issue is duplicate.

#55