Support Ruby 2.2

The syck engine and YAML::ENGINE will be removed.
https://bugs.ruby-lang.org/issues/8344
Convert specs to RSpec 3.0.2 syntax with Transpec

This conversion is done by Transpec 2.3.6 with the following command:
    transpec -f

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

* 90 conversions
    from: == expected
      to: eq(expected)

* 16 conversions
    from: obj.should_receive(:message)
      to: expect(obj).to receive(:message)

* 13 conversions
    from: be_false
      to: be_falsey

* 7 conversions
    from: be_true
      to: be_truthy

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

* 4 conversions
    from: obj.should_not_receive(:message)
      to: expect(obj).not_to receive(:message)

* 2 conversions
    from: lambda { }.should
      to: expect { }.to

* 1 conversion
    from: =~ [1, 2]
      to: match_array([1, 2])

* 1 conversion
    from: obj.stub(:message)
      to: allow(obj).to receive(:message)

For more details: https://github.com/yujinakayama/transpec#supported-conversions
Merge branch 'ruby22' of github.com:eagletmt/safe_yaml into eagletmt-ruby22
added Ruby 2.1 versions for testing
Merge branch 'eagletmt-ruby22'
Merge branch 'rspec3' of github.com:eagletmt/safe_yaml into eagletmt-rspec3
made RSpec output less verbose
Merge branch 'eagletmt-rspec3'