Regenerate gemspec with oauth2 dependency (among other things)

In a Rails project with no pre-existing dependency on the `oauth2` gem, I get errors on startup after adding `ruby-box` to the `Gemfile`. This is ultimately due to the fact that `ruby-box` does not declare its dependency on `oauth2` in the gemspec.

Regenerating the gemspec with `bundle exec rake gemspec` cleared up this issue.