Fix mistranslation in ja/guide/index.md (#191)
Fix mistranslation in ja/guide/index.md (#191)

The original document says:
    `e.target` is the originating element. This is not necessarily the same as `currentTarget`.

But the previous version
    `e.target`はイベントの送信元エレメントです。これは必ずしも必要ではなく、`currentTarget`と同じです。
means the opposite:
    `e.target` is the originating element. This is not necessary and is same as `currentTarget`.

This commit fixes the mistranslation.
riot/riot.github.io,riot/riot.github.io,riot/riot.github.io