Hide toolbar, when PBWebViewController will disappear.

When I popped a PBWebViewController, the ``navigationConroller.toolbar`` is still appearing.

![issue.gif](http://gyazo.com/05de5ecd16200f899eb64684d3f08974.gif)

![ios 7 0 11a465 2013-10-21 16-20-02](https://f.cloud.github.com/assets/19714/1370492/34744086-3a21-11e3-9bd7-d7ad38409203.jpg)

I suggest that calling ``[self.navigationController setToolbarHidden:YES animated:YES]; ``, when PBWebViewController will disappear.