Update index.js

Unless router verb path uses full url, nested routers will not actually match.
I'm going to merge this in, but add a bit more logic around how to trim the path so that it matches how Express' [`.use()` handles prefixes](https://github.com/visionmedia/express/blob/4fe1073f105dbc3b8aa00adf33aa5a19f248117c/lib/router/index.js#L232-270).