Add VPN block and active probing of obfs2. [(diff)](https://trac.torproject.org/projects/tor/wiki/doc/OONI/censorshipwiki/CensorshipByCountry/China?action=diff&version=5) URL: https://trac.torproject.org/projects/tor/wiki/doc/OONI/censorshipwiki/CensorshipByCountry/China?version=5