I struggled with this for a while, updating Ruby 2.0.
It was fixed to install nokigiri using apt-get
apt-get install ruby-nokogiri
As dependencies of third-party notes can be seen using
$ gem dependency nokogiri Gem nokogiri-1.6.1 hoe (~> 3.7, development) hoe-bundler (>= 1.1, development) hoe-debugging (>= 1.0.3, development) hoe-gemspec (>= 1.0, development) hoe-git (>= 1.4, development) mini_portile (~> 0.5.0) minitest (~> 2.2.2, development) racc (>= 1.4.6, development) rake (>= 0.9, development) rake-compiler (~> 0.8.0, development) rdoc (~> 4.0, development) rexical (>= 1.0.5, development)
James McGuigan
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