Test against all the rubies

RBX does not support kwargs yet, and JRuby support for UTF8 source
encoding is wonky in travis.
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