install bundler-1.3 before installing Ruby 2.0! That should downgrade RubyGems to a point that you can just do a gem install bundler to obtain 1.3. Once you begin installing gems with 1.3, everything in Ruby 2.0 will work out again.
articles tagged bundler
Ruby is all about simplicity. Make simple things simple, right? So how come we have to deal with all this complexity when we run Ruby? This is how I made my life slightly easier and got some really sweet benefits as a result.