Will not added the root path

Routes:

``` js
<Route>
  <Route path='/' />
  <Route path='/about' />
</Route>
```

Expected list of paths: `['/', '/about']`
Result: `['/about']`

Error in [`pathsBuilder`](https://github.com/kuflash/react-router-sitemap/blob/master/lib/routes-parser/path-builder.js#L5) module. Incorrect RegExp rule for delete end `/`
