Recibo el siguiente error al migrar a Heroku.

Installing hoe (2.9.4) /usr/ruby1.9.2/lib/ruby/1.9.1/rubygems/installer.rb:170:in >install ': hoe requiere la versión RubyGems> = 1.4. Prueba 'gem update --system' para actualizar RubyGems. (Gema :: InstallError)

Es decir que la versión de ruby gems no está actualizada. ¿Alguien sabe cómo podría resolver este problema?

using rails 3.0.5 con ruby 1.9.2

bundler

Using rake (0.8.7) 
Using RedCloth (4.2.2) 
Using abstract (1.0.0) 
Using activesupport (3.0.5) 
Using builder (2.1.2) 
Using i18n (0.5.0) 
Using activemodel (3.0.5) 
Using erubis (2.6.6) 
Using rack (1.2.2) 
Using rack-mount (0.6.14) 
Using rack-test (0.5.7) 
Using tzinfo (0.3.26) 
Using actionpack (3.0.5) 
Using mime-types (1.16) 
Using polyglot (0.3.1) 
Using treetop (1.4.9) 
Using mail (2.2.17) 
Using actionmailer (3.0.5) 
Using arel (2.0.9) 
Using activerecord (3.0.5) 
Using activeresource (3.0.5) 
Using archive-tar-minitar (0.5.2) 
Using authlogic (2.1.6) 
Using xml-simple (1.0.15) 
Using aws-s3 (0.6.2) 
Using bcrypt-ruby (2.1.4) 
Using block_helpers (0.3.3) 
Using bundler (1.0.10) 
Using columnize (0.3.2) 
Using diff-lcs (1.1.2) 
Using json (1.5.1) 
Using gherkin (2.3.6) 
Using term-ansicolor (1.0.5) 
Using cucumber (0.10.2) 
Using nokogiri (1.4.4) 
Using cucumber-rails (0.4.1) 
Using daemons (1.0.10) 
Using database_cleaner (0.6.7) 
Using factory_girl (1.3.3) 
Using faker (0.9.5) 
Using fastercsv (1.5.4) 
Using formtastic (1.2.3) 
Using gem_plugin (0.2.3) 
Using haml (3.0.25) 
Using hoe (2.9.4) 
Using thor (0.14.6) 
Using railties (3.0.5) 
Using rails (3.0.5) 
Using kaminari (0.12.0) 
Using ruby_core_source (0.1.5) 
Using linecache19 (0.5.12) 
Using meta_search (1.0.4) 
Using mongrel (1.2.0.pre2) 
Using paperclip (2.3.11) 
Using pg (0.11.0) 
Using pickle (0.4.7) 
Using populator (1.0.0) 
Using render_inheritable (1.0.0) 
Using rspec-core (2.5.1) 
Using rspec-expectations (2.5.0) 
Using rspec-mocks (2.5.0) 
Using rspec (2.5.0) 
Using rspec-rails (2.5.0) 
Using ruby-debug-base19 (0.11.25) 
Using ruby-debug19 (0.11.6) 
Using test-unit (1.2.3) 
Using will_paginate (3.0.pre2) 
Using typus (3.0.10) from https://github.com/fesplugas/typus.git (at master) 
Using webrat (0.7.3)

ACTUALIZAR

heroku stack

aspen-mri-1.8.6
* bamboo-ree-1.8.7
bamboo-mri-1.9.2 (prepared, will migrate on next git push)

ACTUALIZACIÓN2:

error trace

Installing hoe (2.9.4) /usr/ruby1.9.2/lib/ruby/1.9.1/rubygems/installer.rb:170:in `install': hoe requires RubyGems version >= 1.4. Try 'gem update --system' to update RubyGems itself. (Gem::InstallError)
    from /usr/ruby1.9.2/lib/ruby/gems/1.9.1/gems/bundler-1.0.7/lib/bundler/source.rb:95:in `install'
    from /usr/ruby1.9.2/lib/ruby/gems/1.9.1/gems/bundler-1.0.7/lib/bundler/installer.rb:55:in `block in run'
    from /usr/ruby1.9.2/lib/ruby/gems/1.9.1/gems/bundler-1.0.7/lib/bundler/spec_set.rb:12:in `block in each'
    from /usr/ruby1.9.2/lib/ruby/gems/1.9.1/gems/bundler-1.0.7/lib/bundler/spec_set.rb:12:in `each'
    from /usr/ruby1.9.2/lib/ruby/gems/1.9.1/gems/bundler-1.0.7/lib/bundler/spec_set.rb:12:in `each'
    from /usr/ruby1.9.2/lib/ruby/gems/1.9.1/gems/bundler-1.0.7/lib/bundler/installer.rb:44:in `run'
    from /usr/ruby1.9.2/lib/ruby/gems/1.9.1/gems/bundler-1.0.7/lib/bundler/installer.rb:8:in `install'
    from /usr/ruby1.9.2/lib/ruby/gems/1.9.1/gems/bundler-1.0.7/lib/bundler/cli.rb:225:in `install'
    from /usr/ruby1.9.2/lib/ruby/gems/1.9.1/gems/bundler-1.0.7/lib/bundler/vendor/thor/task.rb:22:in `run'
    from /usr/ruby1.9.2/lib/ruby/gems/1.9.1/gems/bundler-1.0.7/lib/bundler/vendor/thor/invocation.rb:118:in `invoke_task'
    from /usr/ruby1.9.2/lib/ruby/gems/1.9.1/gems/bundler-1.0.7/lib/bundler/vendor/thor.rb:246:in `dispatch'
    from /usr/ruby1.9.2/lib/ruby/gems/1.9.1/gems/bundler-1.0.7/lib/bundler/vendor/thor/base.rb:389:in `start'
    from /usr/ruby1.9.2/lib/ruby/gems/1.9.1/gems/bundler-1.0.7/bin/bundle:13:in `<top (required)>'
    from /usr/ruby1.9.2/bin/bundle:19:in `load'
    from /usr/ruby1.9.2/bin/bundle:19:in `<main>'
   FAILED: http://devcenter.heroku.com/articles/bundler
!Heroku push rejected, failed to install gems via Bundler