Given that Bundler 1.10 was released back in 2015, we can assume
that people are at least on this version or a higher one so there
is no need to ask people to upgrade.

Also, given that Rails 5.0 supports Ruby 2.2+ and given that this
version come with Minitest 5.4.3 bundled, we don't need to ensure
backward compatibility with Minitest 4.