Removed separate build instructions for Nokogiri, because its current version is able to build without `use-system-libraries`. Relates to https://github.com/iron-io/dockers/issues/53.
Removed separate build instructions for Nokogiri, because its current version is able to build without `use-system-libraries`.
Relates to https://github.com/iron-io/dockers/issues/53.

iron-io/dockers,iron-io/dockers,iron-io/dockers