Activemerchant requires older version of builder, which conflicts which activemodel?

gistfile1.txt

$ ruby main.rb 
/opt/local/lib/ruby1.9/1.9.1/rubygems/specification.rb:1637:in `raise_if_conflicts': Unable to activate activemodel-3.2.12, because builder-3.2.0 conflicts with builder (~> 3.0.0) (Gem::LoadError)
        from /opt/local/lib/ruby1.9/1.9.1/rubygems/specification.rb:746:in `activate'
        from /opt/local/lib/ruby1.9/1.9.1/rubygems/specification.rb:780:in `block in activate_dependencies'
        from /opt/local/lib/ruby1.9/1.9.1/rubygems/specification.rb:766:in `each'
        from /opt/local/lib/ruby1.9/1.9.1/rubygems/specification.rb:766:in `activate_dependencies'
        from /opt/local/lib/ruby1.9/1.9.1/rubygems/specification.rb:750:in `activate'
        from /opt/local/lib/ruby1.9/1.9.1/rubygems/custom_require.rb:51:in `block in require'
        from /opt/local/lib/ruby1.9/1.9.1/rubygems/custom_require.rb:50:in `each'
        from /opt/local/lib/ruby1.9/1.9.1/rubygems/custom_require.rb:50:in `require'
        from /opt/local/lib/ruby1.9/gems/1.9.1/gems/sinatra-activerecord-1.2.2/lib/sinatra/activerecord.rb:2:in `<top (required)>'
        from /opt/local/lib/ruby1.9/1.9.1/rubygems/custom_require.rb:60:in `require'
        from /opt/local/lib/ruby1.9/1.9.1/rubygems/custom_require.rb:60:in `rescue in require'
        from /opt/local/lib/ruby1.9/1.9.1/rubygems/custom_require.rb:35:in `require'
        from main.rb:9:in `<main>'

gistfile2.yml

GEM
  remote: http://rubygems.org/
  specs:
    active_utils (1.0.5)
      activesupport (>= 2.3.11)
      i18n
    activemerchant (1.31.1)
      active_utils (>= 1.0.2)
      activesupport (>= 2.3.14)
      builder (>= 2.0.0) # Buidler 1.
      i18n
      json (>= 1.5.1)
      money
      nokogiri
    activemodel (3.2.12)
      activesupport (= 3.2.12)
      builder (~> 3.0.0) # Builder 2.
    activerecord (3.2.12)
      activemodel (= 3.2.12)
      activesupport (= 3.2.12)
      arel (~> 3.0.2)
      tzinfo (~> 0.3.29)
    activesupport (3.2.12)
      i18n (~> 0.6)
      multi_json (~> 1.0)
    arel (3.0.2)
    builder (3.0.4) # Builder 3.
    excon (0.16.10)
    i18n (0.6.4)
    json (1.7.7)
    mandrill-api (1.0.16)
      excon (~> 0.16.0)
      json (~> 1.7.7)
    money (5.1.1)
      i18n (~> 0.6.0)
    multi_json (1.6.1)
    nokogiri (1.5.6)
    rack (1.5.2)
    rack-flash3 (1.0.3)
      rack
      rack
    rack-protection (1.4.0)
      rack
    rake (10.0.3)
    sinatra (1.3.5)
      rack (~> 1.4)
      rack-protection (~> 1.3)
      tilt (~> 1.3, >= 1.3.3)
    sinatra-activerecord (1.2.2)
      activerecord (~> 3.0)
      sinatra (~> 1.0)
    sqlite3 (1.3.7)
    tilt (1.3.4)
    tzinfo (0.3.36)
    validatable (1.6.7)

PLATFORMS
  ruby

DEPENDENCIES
  activemerchant
  activerecord
  activesupport
  mandrill-api
  rack-flash3
  rake
  sinatra
  sinatra-activerecord
  sqlite3
  tzinfo
  validatable