Windows Rubyでgem install jsonを実行するとエラーになる

Windows Rubyでgem install jsonを実行するとエラーになる Please login or register to vote for this post. (click on this box to dismiss) 1) Download Ruby 1.9.3-p0 2) Download DevKit file from http://rubyinstaller.org/downloads (DevKit-tdm-32-4.5.2-20110712-1620-sfx.exe) 3) Extract DevKit to path C:\Ruby193\DevKit 4) cd C:\Ruby193\DevKit 5) ruby dk.rb init 6) ruby dk.rb review 7) ruby dk.rb install