Fix bug where URI path is to a file and not to directory

[dekelyi]

When trying to access the website page via domain.example/index.html instead of domain.example, docsify is trying to read the markdown files relative to index.html as he thinks this is a directory, which result in HTTP 404 Error.

docsify.min.js:1 GET localhost/index.html/README.md 404 (Not Found)

Please fix and thank you for your awesome documentation generator.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.