title: cannot load such file -- sass/cache_stores
body: <p>I'm working on a rails 3.2 app and have started getting these errors relating to cache_stores.</p>
  
  <pre><code>% rake --trace             
  rake aborted!
  cannot load such file -- sass/cache_stores
  /home/map7/.rbenv/versions/1.9.3-p125/lib/ruby/gems/1.9.1/gems/sass-3.1.10/lib/sass/engine.rb:4:in `require'
  /home/map7/.rbenv/versions/1.9.3-p125/lib/ruby/gems/1.9.1/gems/sass-3.1.10/lib/sass/engine.rb:4:in `&lt;top (required)&gt;'
  /home/map7/.rbenv/versions/1.9.3-p125/lib/ruby/gems/1.9.1/gems/sass-3.1.10/lib/sass.rb:71:in `require'
  /home/map7/.rbenv/versions/1.9.3-p125/lib/ruby/gems/1.9.1/gems/sass-3.1.10/lib/sass.rb:71:in `&lt;top (required)&gt;'
  /home/map7/.rbenv/versions/1.9.3-p125/lib/ruby/gems/1.9.1/gems/bundler-1.1.4/lib/bundler/runtime.rb:68:in `require'
  /home/map7/.rbenv/versions/1.9.3-p125/lib/ruby/gems/1.9.1/gems/bundler-1.1.4/lib/bundler/runtime.rb:68:in `block (2 levels) in require'
  /home/map7/.rbenv/versions/1.9.3-p125/lib/ruby/gems/1.9.1/gems/bundler-1.1.4/lib/bundler/runtime.rb:66:in `each'
  /home/map7/.rbenv/versions/1.9.3-p125/lib/ruby/gems/1.9.1/gems/bundler-1.1.4/lib/bundler/runtime.rb:66:in `block in require'
  /home/map7/.rbenv/versions/1.9.3-p125/lib/ruby/gems/1.9.1/gems/bundler-1.1.4/lib/bundler/runtime.rb:55:in `each'
  /home/map7/.rbenv/versions/1.9.3-p125/lib/ruby/gems/1.9.1/gems/bundler-1.1.4/lib/bundler/runtime.rb:55:in `require'
  /home/map7/.rbenv/versions/1.9.3-p125/lib/ruby/gems/1.9.1/gems/bundler-1.1.4/lib/bundler.rb:119:in `require'
  /home/map7/project/config/application.rb:11:in `&lt;top (required)&gt;'
  /home/map7/project/Rakefile:4:in `require'
  /home/map7/project/Rakefile:4:in `&lt;top (required)&gt;'
  /home/map7/.rbenv/versions/1.9.3-p125/lib/ruby/1.9.1/rake/rake_module.rb:25:in `load'
  /home/map7/.rbenv/versions/1.9.3-p125/lib/ruby/1.9.1/rake/rake_module.rb:25:in `load_rakefile'
  /home/map7/.rbenv/versions/1.9.3-p125/lib/ruby/1.9.1/rake/application.rb:501:in `raw_load_rakefile'
  /home/map7/.rbenv/versions/1.9.3-p125/lib/ruby/1.9.1/rake/application.rb:82:in `block in load_rakefile'
  /home/map7/.rbenv/versions/1.9.3-p125/lib/ruby/1.9.1/rake/application.rb:133:in `standard_exception_handling'
  /home/map7/.rbenv/versions/1.9.3-p125/lib/ruby/1.9.1/rake/application.rb:81:in `load_rakefile'
  /home/map7/.rbenv/versions/1.9.3-p125/lib/ruby/1.9.1/rake/application.rb:65:in `block in run'
  /home/map7/.rbenv/versions/1.9.3-p125/lib/ruby/1.9.1/rake/application.rb:133:in `standard_exception_handling'
  /home/map7/.rbenv/versions/1.9.3-p125/lib/ruby/1.9.1/rake/application.rb:63:in `run'
  /home/map7/.rbenv/versions/1.9.3-p125/bin/rake:32:in `&lt;main&gt;'
  </code></pre>
  
  <p>I've tried running bundle update.</p>