Replace tor-experimental-0.3.0.x with tor-nightly-master on the debian page
We tell people to use the Tor 0.3.0 packages for the development branch: https://www.torproject.org/docs/debian.html.en#development https://www.torproject.org/docs/debian.html.en#source
But Tor 0.3.0 will not be supported on 1 February 2018.
To avoid changing this every 6 months, let's use tor-nightly-master-DISTRIBUTION instead.