Dotty logo image on documentation site is now missing/broken link

Since the renaming of artifacts to scala3-*, the Dotty logo in the header atop the [documentation/blog site](http://dotty.epfl.ch/docs/index.html) is a broken image ([http://dotty.epfl.ch/images/scala3-logo.svg](http://dotty.epfl.ch/images/scala3-logo.svg) gives a 404 Error)
