changed rails version to 4.1.0 in Gemfile and ran 'bundle update rails simple_form slim-rails' which was the minimal set of gems that needed to be updated in order for bundle update to succeed
changes for Rails 4.1 based on comparison to freshly generated Rails 4.1 project
Gemfile changes based on sample rails-bootstrap project for Rails 4.1 at GitHub: RailsApps/rails-bootstrap
regenerated Gemfile.lock, including resolving versioning issue with sprockets (now at 2.11.0)
specs running and passing with Rails 4.1; added trivial Topic spec to models
Merge pull request #10 from Jan-Hettich/rails41

Upgrade to Rails 4.1