gemspec instead of Gemfile
be_true -> be_truthy
avoid I18n deprecation warning
use Rails 4
Convert specs to RSpec 3.0.2 syntax with Transpec

This conversion is done by Transpec 2.3.1 with the following command:
    transpec -f

* 61 conversions
    from: obj.should
      to: expect(obj).to

* 4 conversions
    from: obj.should_not
      to: expect(obj).not_to

For more details: https://github.com/yujinakayama/transpec#supported-conversions
Make travis happy again.

Remove testing on master for now.