$ sudo apt-get install mecab libmecab-dev
$ wget http://jaist.dl.sourceforge.net/sourceforge/mecab/mecab-ruby-0.98.tar.gz
$ tar zxvf mecab-ruby-0.98.tar.gz
$ cd mecab-ruby-0.98
$ gem build mecab-ruby.gemspec
$ sudo gem install mecab-ruby-0.97.gem

libmecab-dev 入れてなくてはまった