executable isn't being distributed with gem

```
gem install yamldiff -V
GET https://api.rubygems.org/latest_specs.4.8.gz
302 Moved Temporarily
GET https://s3.amazonaws.com/production.s3.rubygems.org/latest_specs.4.8.gz
200 OK
HEAD https://api.rubygems.org/api/v1/dependencies
200 OK
GET https://api.rubygems.org/api/v1/dependencies?gems=yamldiff
200 OK
/Users/drnic/.rvm/gems/ruby-2.0.0-p451/gems/yamldiff-0.0.8/.gitignore
/Users/drnic/.rvm/gems/ruby-2.0.0-p451/gems/yamldiff-0.0.8/Gemfile
/Users/drnic/.rvm/gems/ruby-2.0.0-p451/gems/yamldiff-0.0.8/LICENSE
/Users/drnic/.rvm/gems/ruby-2.0.0-p451/gems/yamldiff-0.0.8/README.md
/Users/drnic/.rvm/gems/ruby-2.0.0-p451/gems/yamldiff-0.0.8/Rakefile
/Users/drnic/.rvm/gems/ruby-2.0.0-p451/gems/yamldiff-0.0.8/lib/yamldiff.rb
/Users/drnic/.rvm/gems/ruby-2.0.0-p451/gems/yamldiff-0.0.8/lib/yamldiff/version.rb
/Users/drnic/.rvm/gems/ruby-2.0.0-p451/gems/yamldiff-0.0.8/lib/yamldiff/yamldiff.rb
/Users/drnic/.rvm/gems/ruby-2.0.0-p451/gems/yamldiff-0.0.8/lib/yamldiff/yamldiff_error.rb
/Users/drnic/.rvm/gems/ruby-2.0.0-p451/gems/yamldiff-0.0.8/spec/lib/yamldiff_spec.rb
/Users/drnic/.rvm/gems/ruby-2.0.0-p451/gems/yamldiff-0.0.8/spec/spec_helper.rb
/Users/drnic/.rvm/gems/ruby-2.0.0-p451/gems/yamldiff-0.0.8/yamldiff.gemspec
Successfully installed yamldiff-0.0.8
Parsing documentation for yamldiff-0.0.8
Parsing sources...
100% [ 4/ 4]  lib/yamldiff/yamldiff_error.rb                                    
1 gem installed
```

Missing the `bin/yamldiff`