warning: assigned but unused variable - method_name_with_spork

running tests `rake test` on a rails project we have started seeing this warning: 

/Users/xxx/.rvm/gems/ruby-2.2.4@projectname/gems/spork-1.0.0rc4/lib/spork.rb:83: warning: assigned but unused variable - method_name_with_spork

https://github.com/sporkrb/spork/blob/master/lib/spork.rb#L83

We can ignore warnings in multiple ways but wanted to at least notify this project about it.
