ubuntu 12.04 gem install rmagick -v '2.13.2' 失敗
https://github.com/rmagick/rmagick
https://www.ruby-toolbox.com/categories/image_processing
http://stackoverflow.com/questions/3704919/installing-rmagick-on-ubuntu
gem install rmagick -v '2.13.2'
で失敗した時は
sudo apt-get install imagemagick libmagickwand-dev