Probable glitch in the thumb-tile icon url

Opening the *Advanced...* action of the workflow *State* submenu I see a broken image just before the title of the interested contents.

There is what seems a spurious single quote in the [expression](https://github.com/plone/plone.app.content/blob/master/plone/app/content/browser/templates/content_status_history.pt#L161) that computes the `thumb-tile` icon in the `content_status_history.pt`. 
