use stronger boolean rspec matchers
remove unneeded custom matcher
remove unused dependency
Convert specs to RSpec 3.0.3 syntax with Transpec

This conversion is done by Transpec 2.3.6 with the following command:
    transpec -b true,false -f -s

* 11 conversions
    from: it { should ... }
      to: it { is_expected.to ... }

* 1 conversion
    from: obj.should
      to: expect(obj).to

For more details: https://github.com/yujinakayama/transpec#supported-conversions
Merge pull request #206 from tamird/stronger_boolean_matchers

spec cleanup