Test against all the rubies

RBX does not support kwargs yet.
Convert specs to RSpec 3.1.5 syntax with Transpec

This conversion is done by Transpec 2.3.7 with the following command:
    transpec -b true,false -f

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

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

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

* 3 conversions
    from: obj.stub(:message)
      to: allow(obj).to receive(:message)

* 1 conversion
    from: lambda { }.should
      to: expect { }.to

For more details: https://github.com/yujinakayama/transpec#supported-conversions
Add Rubocop
Lint/BlockAlignment
Lint/RescueException
Style/Alias
Style/Blocks
Style/BracesAroundHashParameters
Style/CollectionMethods
Style/CommentIndentation
Style/EmptyLines
Style/EmptyLinesAroundBody
Style/HashSyntax
Style/IndentHash
Style/IndentationConsistency
Style/IndentationWidth
Style/LeadingCommentSpace
Style/NegatedIf
Style/NegatedWhile
Style/NumericLiterals