avoid name clash with Object.clone method

using rubocop in the same Rakefile yields

```
bundle exec rake rubocop
Running RuboCop...
Inspecting 10 files
private method `clone' called for #<RuboCop::Cop::CopStore:0x000001045a8250>
/Users/ehaselwanter/.rvm/gems/ruby-2.1.1/gems/rubocop-0.23.0/lib/rubocop/cop/cop.rb:57:in `all'
/Users/ehaselwanter/.rvm/gems/ruby-2.1.1/gems/rubocop-0.23.0/lib/rubocop/file_inspector.rb:114:in `mobilized_cop_classes'
/Users/ehaselwanter/.rvm/gems/ruby-2.1.1/gems/rubocop-0.23.0/lib/rubocop/file_inspector.rb:105:in `inspect_file'
/Users/ehaselwanter/.rvm/gems/ruby-2.1.1/gems/rubocop-0.23.0/lib/rubocop/file_inspector.rb:74:in `block in pr
```