Fix for ruby 2.0.

For some reason on Ruby 2.0, we were getting this error:

  TypeError:
       compared with non class/module
     # ./lib/rspec/mocks/instance_method_stasher.rb:73:in `define_method'
     # ./lib/rspec/mocks/instance_method_stasher.rb:73:in `restore'
     # ./lib/rspec/mocks/method_double.rb:74:in `restore_original_method'
     # ./lib/rspec/mocks/method_double.rb:94:in `reset'
     # ./lib/rspec/mocks/proxy.rb:123:in `block in reset'
     # ./lib/rspec/mocks/proxy.rb:123:in `each'
     # ./lib/rspec/mocks/proxy.rb:123:in `reset'
     # ./lib/rspec/mocks/proxy.rb:118:in `verify'
     # ./lib/rspec/mocks/space.rb:14:in `block in verify_all'
     # ./lib/rspec/mocks/space.rb:13:in `each_value'
     # ./lib/rspec/mocks/space.rb:13:in `verify_all'
     # ./lib/rspec/mocks.rb:18:in `verify'