broken link to usage

There's a link in the docs on this page [usage](http://lesscss.org/usage/#using-less) that uses `<a href="{{resolve 'index'}}/#using-less">` within
[usage.hbs](https://github.com/less/less-docs/blob/master/templates/usage.hbs#L11). That link should be rendering `http://lesscss.org/#using-less` but it's rendering `http://lesscss.org/index.html/#using-less`. Since it's rendering to `index.html` and it's not removing the `path.extname` I can assume that It's because it's not finding it in resolves `pages` loop. I'm not sure how to fix it with `hbs`. But this does the trick.