Bundler couldn't find compatible versions for gem "rails" using PayPal adaptive_payments_samples

Getting the following error when trying to install the "adaptive_payments_samples" gem: https://github.com/paypal/adaptivepayments-sdk-ruby/tree/master/samples

I am not sure which gem I am missing or what addiction problem I should be solving. Updated the package but it didn't help.

Bundler could not find compatible versions for gem "rails":
  In snapshot (Gemfile.lock):
    rails (= 4.2.3)

  In Gemfile:
    rails-assets-cdn (>= 0) ruby depends on
      rails (>= 0) ruby

    rails-assets-cdn (>= 0) ruby depends on
      rails (>= 0) ruby

    griddler-mandrill (>= 0) ruby depends on
      griddler (>= 1.2.1) ruby depends on
        rails (>= 3.2.0) ruby

    adaptive_payments_samples (>= 0) ruby depends on
      rails (~> 3.2.9) ruby

    rails (~> 4.2.3) ruby

Running `bundle update` will rebuild your snapshot from scratch, using only
the gems in your Gemfile, which may resolve the conflict.