Sass broken after install with RVM, using Assetic PHP

问题

I'm trying to set up Assetic PHP asset compiler and I have got it working with CoffeeScript, Stylus, and Less (all the NPM packages worked perfectly). However, with Sass I am having a problem. Here are the steps I've taken so far:

I installed RVM along with Ruby 1.9.3 and ran gem install sass.
I ran which sass. This returned /home/jon/.rvm/gems/ruby-1.9.3-p0/bin/sass.
I copied that location into SassFilter.php in Assetic where it says $sassPath = '' in the constructor function. This is the same way I did Coffee, etc.

Now when I parse PHP from my main compiler file, I get this message:

PHP Fatal error:  Uncaught exception 'RuntimeException' with message '/home/jon/.rvm/rubies/ruby-1.9.3-p0/lib/ruby/site_ruby/1.9.1/rubygems/dependency.rb:247:in `to_specs': Could not find sass (>= 0) amongst [bigdecimal-1.1.0, io-console-0.3, json-1.5.4, minitest-2.5.1, rake-0.9.2.2, rdoc-3.9.4] (Gem::LoadError)
from /home/jon/.rvm/rubies/ruby-1.9.3-p0/lib/ruby/site_ruby/1.9.1/rubygems/dependency.rb:256:in `to_spec'
from /home/jon/.rvm/rubies/ruby-1.9.3-p0/lib/ruby/site_ruby/1.9.1/rubygems.rb:1208:in `gem'
from /home/jon/.rvm/gems/ruby-1.9.3-p0/bin/sass:18:in `<main>'
' in /home/jon/www/compilers/Assetic/Filter/Sass/SassFilter.php:158
Stack trace:
#0 /home/jon/www/compilers/Assetic/Filter/FilterCollection.php(62): Assetic\Filter\Sass\SassFilter->filterLoad(Object(Assetic\Asset\FileAsset))
#1 /home/jon/www/compilers/Assetic/Asset/BaseAsset.php(83): Assetic\Filter\FilterCollection->filterLoad(Object(Assetic\Asset\FileAsset))
#2 /home/jon/www/compilers/Assetic/Asset/FileAsset.php(57): Asseti in /home/jon/www/compilers/Assetic/Filter/Sass/SassFilter.php on line 158

I am using Ubuntu 11.10, PHP 5.3.6, RVM 1.10.2, and Ruby 1.9.3. My shell is ZSH.