undefined method `default_mime_type=' for Sprockets::JstProcessor:Class (NoMethodError)

[noahcampbell]

I installed on a mac book pro

$ sudo gem install jasmine-headless-webkit
Password:
Building native extensions.  This could take a while...
Successfully installed jasmine-headless-webkit-0.8.4
1 gem installed
Installing ri documentation for jasmine-headless-webkit-0.8.4...
Installing RDoc documentation for jasmine-headless-webkit-0.8.4...

When I run jasmine-headless-webkit from the command line, I get the following:

$ jasmine-headless-webkit [jasmine-headless-webkit] undefined method `default_mime_type=' for Sprockets::JstProcessor:Class (NoMethodError)
  /Library/Ruby/Gems/1.8/gems/sprockets-2.10.0/lib/sprockets/jst_processor.rb:5
  /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems/custom_require.rb:31:in `gem_original_require'
  /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems/custom_require.rb:31:in `require'
  /Library/Ruby/Gems/1.8/gems/sprockets-2.10.0/lib/sprockets/engines.rb:3
  /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems/custom_require.rb:31:in `gem_original_require'
  /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems/custom_require.rb:31:in `require'
  /Library/Ruby/Gems/1.8/gems/sprockets-2.10.0/lib/sprockets.rb:44
  /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems/custom_require.rb:31:in `gem_original_require'
  /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems/custom_require.rb:31:in `require'
  /Library/Ruby/Gems/1.8/gems/jasmine-headless-webkit-0.8.4/lib/jasmine/headless/runner.rb:7
  /Library/Ruby/Gems/1.8/gems/jasmine-headless-webkit-0.8.4/lib/jasmine/headless/command_line.rb:10:in `run!'
  /Library/Ruby/Gems/1.8/gems/jasmine-headless-webkit-0.8.4/bin/jasmine-headless-webkit:10
  /usr/bin/jasmine-headless-webkit:19:in `load'
  /usr/bin/jasmine-headless-webkit:19

Please ask me any questions, I'm not a ruby developer, I want to run a test suite for a javascript library.