Add ruby language

[h-bragg]

Basically: follow https://github.com/rubocop-hq/ruby-style-guide
Could add some stuff for development / gem?

[biggianteye]

I recently ran rubycop over some of the ruby we have, specifically the stuff derived from cucumber-api and there were a number of useful best practise and deprecation recommendations. Given that we have some ruby (albeit a small amount) I think it makes sense to have some standards for it.

Hooking up rubycop to build pipelines would also be useful, but that's tangential to this issue.