Exception when no root specified

We're used to always having '/partners' - but when no root is specified (and it defaults to `""`), you get an invalid RegEx from this guy:

```
  /**
  @method _removeURIRoot
  @param {String} uri '/partners/s/foo-bar'
  @return {String} uri '/s/foo-bar'
  **/
  _removeURIRoot: function (uri) {
    var rootRegex = new RegExp('^' + this.root);

    return uri.replace(rootRegex, '');
  }
```
