Fix gemspec to not need Gemfile.lock

Otherwise you get this error:

    klomp at /Users/matt/.rbenv/versions/1.9.3-p484/lib/ruby/gems/1.9.1/bundler/gems/klomp-eb1749b1e581 did not have a valid gemspec.
    This prevents bundler from installing bins or native extensions, but that may not affect its functionality.
    The validation message from Rubygems was:
      ["Gemfile.lock"] are not files