Remove Gemfile.lock

It's recommended to not include Gemfile.lock in the repo for gems. It locks gem developers to specific dependency versions, when they ought to have the flexibility to install whatever versions are specified in the .gemspec.

Good explanation here:
http://yehudakatz.com/2010/12/16/clarifying-the-roles-of-the-gemspec-and-gemfile/

The Gemfile.lock also makes Gemnasium think the RDF dependencies are out-of-date:
https://gemnasium.com/ruby-rdf/rdf