Created by: seanpdoyle
The appraisal install command does not (yet?) accept flags in the same
way that bundle install does.
Prior to this commit, bundle install --path vendor/bundle is invoked
between restoring from and saving to the cache. In theory, this
relies on prior installation work.
Unfortunately, since the test suite is run through Appraisals, these caches are unused.
This commit replaces the appraisal install with the underlying
behavior, called explicitly by setting BUNDLE_GEMFILE directly for
each supported Rails version.