Error: rubygems/core_ext/kernel_require.rb:121:in `require': cannot load such file

Hi. I try to install your gem, but it exit with error:

```
/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:121:in `require': cannot load such file -- facets/enumerable/group_by (LoadError)
```

Ruby 2.1.0
OS X 10.10.2
