Enable specifying --path in bundle install on Ruby docker images

Upstream docker images for Ruby now has https://github.com/docker-library/ruby/pull/285,, which disables passing --path to bundle install. This broke our CI, since we need to specify a path for caching.

The alternative is to specify it as BUNDLE_PATH, but currently there is a bug which won't persist it in .bundle/config, and thus is lost between before_script and script. So, temporarily, we are reverting the upstream change manually.