Use replace when "correcting" hashbangs

[frolic]

https://github.com/vuejs/vue-router/blob/master/src/index.js#L158

If I have hashbangs enabled and I navigate to a URL like /#/some/path, it gets corrected to /!#/some/path. However, the correction adds an entry to the history, essentially breaking the back button (because going back immediately redirects to the same page again).

It looks like we can take advantage of history.replaceState to overcome this:
http://stackoverflow.com/a/9282379/143455

Alternatively, location.replace may work too (although I'm not sure if the hash change will affect the DOM if the router-view doesn't actually change).