Generates the first index.html without blog directory

[kiarafbickers]

When you modify the root _config.yml file to include:

index_generator:
  path: ''
  per_page: 10
  order_by: -date

It creates blog pages without the first numbered index.

INFO  Generated: index.html
INFO  Generated: blog/2/index.html
INFO  Generated: blog/3/index.html
INFO  Generated: blog/4/index.html
INFO  Generated: blog/5/index.html

The first blog page should be blog/1/index.html instead of index.html.

[stevenjoezhang]

See https://github.com/hexojs/hexo-pagination/blob/b55476aba501102b6f7e86b61713b125962d8b39/lib/pagination.js#L27