Fix gem related tiny issues

Hi, I have found some issues related gem.
- Delete Gemfile.lock
  - Gemfile.lock has been ignored in .gitignore but it remains.
- Correct indents
- Add License
  - I think it is Apache License, Version 2.0
- Add `rake` for `bundle exec rake test`
  - Bundler needs rake
- Change homepage to github from rubyforge