compass compileで"LoadError on line ["55"]"というエラーが出たので対応．

# compass compileで"LoadError on line ["55"]"というエラーが出たので対応．
# 参考: LoadError on line [“55”] of C: cannot load such file — wdm Run with --trace to see the full backtrace

# error
$ compass compile
> LoadError on line ["55"] of /usr/local/rbenv/versions/2.0.0-p353/lib/ruby/site_ruby/2.0.0/rubygems/core_ext/kernel_require.rb: cannot load such file -- compass/import-once/activate
> Run with --trace to see the full backtrace

# success
$ gem uninstall sass
$ gem uninstall compass
$ gem install sass
$ gem install compass
$ compass compile