fix error

$ knife solo init chef-repo -VV
Creating kitchen...
Creating knife.rb in kitchen...
/usr/lib/ruby/gems/1.8/gems/knife-solo-0.3.0.pre4/lib/knife-solo.rb:5:in `resource': uninitialized constant KnifeSolo::Pathname (NameError)
        from /usr/lib/ruby/gems/1.8/gems/knife-solo-0.3.0.pre4/lib/chef/knife/solo_init.rb:62:in `create_config'
        from /usr/lib/ruby/gems/1.8/gems/knife-solo-0.3.0.pre4/lib/chef/knife/solo_init.rb:28:in `run'
        from /usr/lib/ruby/gems/1.8/gems/chef-11.4.0/lib/chef/knife.rb:460:in `run_with_pretty_exceptions'
        from /usr/lib/ruby/gems/1.8/gems/chef-11.4.0/lib/chef/knife.rb:173:in `run'
        from /usr/lib/ruby/gems/1.8/gems/chef-11.4.0/lib/chef/application/knife.rb:123:in `run'
        from /usr/lib/ruby/gems/1.8/gems/chef-11.4.0/bin/knife:25
        from /usr/bin/knife:19:in `load'
        from /usr/bin/knife:19
Merge pull request #230 from kmdsbng/patch-1

Add missing `require` statement