[metrics-team] [tor-relays] New Fallbacks from June 2019

[Damian Johnson]

> Stem also hasn't updated yet, and Stem's list is used for consensus-health:
> https://trac.torproject.org/projects/tor/ticket/31315

Hi teor. If consensus-health desires the present fallbacks it should
use the following. It isn't necessary to wait for stem to re-cache.

try:
  fallbacks = stem.directory.Fallback.from_remote()
except IOError:
  fallbacks = stem.directory.Fallback.from_cache()