Ruby: dig method

https://stackoverflow.com/questions/34346653/how-do-i-use-arraydig-and-hashdig-introduced-in-ruby-2-3
https://www.tiagoamaro.com.br/2016/08/27/ruby-2-3-dig/
http://anamaria.martinezgomez.name/2018/01/07/ruby-dig.html