As described in sparklemotion/nokogiri#1370 there seems to be an issue with the rubygems upgrade to 2.5.0 and installing nokogiri with the overlay driver.

As it seems more a docker issue I would recommend to downgrade to rubygems 2.4.8 for the time being as this will probably affect quite a lot build setups.

The quick fix we are currently doing is run gem update --system '2.4.8' in our Dockerfile.