This change both speeds up specs (less strings to allocate) and helps catch
cases where methods in Discourse are mutating inputs.
Overall we will be migrating everything to use #frozen_string_literal: true
it will take a while, but this is the first and safest move in this direction
This updates tests to use latest rails 5 practice
and updates ALL dependencies that could be updated
Performance testing shows that performance has not regressed
if anything it is marginally faster now.
