Replace The Ruby Racer with Mini Racer (updated)

[deivid-rodriguez]

Hi! This is just the branch we're using at the bundler documentation repository: https://github.com/rubygems/bundler-site, to get this repository working against a newer stack of dependencies.

This is just #36 with one commit on top to allow newer versions of mini_racer.

@matiasgarciaisaia I wonder whether there's any chance of getting some movement here? Thank you! ❤️

[tnir]

@manastech Anyone can take a look at this? 🙏

[deivid-rodriguez]

I'm not too optimistic here :( I even sent a private email to @manastech but I got no reply. We should consider other options.