Unmatched route with root option and popstate event

[sndrgb]

Hi, this was my scenario:

1. route initialized with history option true and root option set to /en like this:

router = new Router({
    history: true,
    root: utils.lang
});

2. navigating from homepage ( /en ) to contact ( /en/contact )

3. clicking back button for come back to homepage ( /en ) matches default '404' route ( * )

after some tries and investigations i think i've found a little bug in /src/history/html5.js p.start method where this.listener function loses its context. i resolve binding the function to this

 this.listener = function (e) {
    var url = decodeURI(location.pathname + location.search)
    if (this.root) {
      url = url.replace(this.rootRE, '')
    }
    self.onChange(url, e && e.state, location.hash)
  }.bind(this);