Chef を gem からインストールしようとすると、下記エラーが出た。 $ sudo gem install chef Building native extensions. This could take a while... ERROR: Error installing chef: ERROR: Failed to build gem native extension. /usr/bin/ruby2.0 extconf.rb creating Makefile /var/lib/gems/2.0.0/gems/libyajl2-1.2.0/ext/libyajl2 extconf.rb:104:in `makemakefiles': unhandled exception from extconf.rb:138:in `<main>' Gem files will remain i