Fixing broken Continue links

See [The Jekyll Docs](http://jekyllrb.com/docs/pagination/); the link
method for the next page is `paginator.next_page_path`, not just
`paginator.next_page`. The old code would happen to work if you stored
your pages as /2, /3, ... etc, but not if you stored them as /posts/2,
/posts/3, as is the Octopress default.