Includes a backwards compatibility mode for SsrfFilter 1.0,
which is needed for Ruby 2.5 and JRuby 9.2.
Also includes a local version constraint for fog-google for
Ruby 2.5 and JRuby 9.2 because of a known but undeclared
incompatibility in that gem. gemfiles/rails-6-1.gemfile
already has this fix.
[Fixes#2625]