Update FakeFS beyond 2.6

[faisal]

FakeFS 2.7 and later fail on JRuby, often in ways that appear to have nothing to do with how RubyCritic is using FakeFS.

Two examples with FakeFS 3.0.0:

expected that command "rubycritic smelly.rb  --no-browser" has exit status of "0", but has "1". (RSpec::Expectations::ExpectationNotMetError)
./features/step_definitions/rubycritic_steps.rb:12:in `/^the exit status indicates a success$/'
/opt/homebrew/Cellar/jruby/9.4.10.0/libexec/bin/jbundle:25:in `<main>'
features/command_line_interface/minimum_score.feature:8:in `the exit status indicates a success'

In CI: Gem::LoadError: You have already activated jar-dependencies 0.4.1, but your Gemfile requires jar-dependencies 0.5.2. Since jar-dependencies is a default gem, you can either remove your dependency on it or try updating to a newer version of bundler that supports jar-dependencies as a default gem. However, jar-depedencies isn't in the Gemfile, and appears to be pulled in via psych, which also isn't declared in the Gemfile.

[faisal]

This PR updates FakeFS to 3.0: #504