Find Jekyll::Converters::Scss

Fix
```
/usr/lib/ruby/vendor_ruby/jekyll/converters/sass.rb:7:in `<module:Converters>': uninitialized constant Jekyll::Converters::Scss (NameError)
	from /usr/lib/ruby/vendor_ruby/jekyll/converters/sass.rb:6:in `<module:Jekyll>'
	from /usr/lib/ruby/vendor_ruby/jekyll/converters/sass.rb:5:in `<top (required)>'
	from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
	from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
	from /usr/lib/ruby/vendor_ruby/jekyll.rb:11:in `block in require_all'
	from /usr/lib/ruby/vendor_ruby/jekyll.rb:10:in `each'
	from /usr/lib/ruby/vendor_ruby/jekyll.rb:10:in `require_all'
	from /usr/lib/ruby/vendor_ruby/jekyll.rb:64:in `<top (required)>'
	from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
	from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
	from /usr/bin/jekyll:6:in `<main>'
```
when running `jekyll` on Ubuntu 14.10.