Do not track Gemfile.lock

Tracking Gemfile.lock for gems is not advised, as RubyGems will not (during the `gem install` process) use this. It is therefore advisable that versions be specified in the gemspec and the Gemfile.lock be untracked.
AddAdd gem dependency versions to gemspec.
Restrict github-pages to one MAJOR version.
Merge pull request #16 from parkr/untrack-gemfile-

Untrack Gemfile.lock & Add Versions to Gemspec