Add specs for `half` option in `Rational#round`
Add specs for `half` option in `Rational#round`

In Ruby 2.4 the `round` method in `Rational` accepts a keyword argument
(`half`). The specs values were based on
https://github.com/ruby/ruby/blob/6b05153a3a75b74b64553d6a46f501d9ee0f0376/rational.c#L1577-L1585
and https://github.com/nilsding/spec/blob/80119090e7cd9071cb52905f13d52ca56b5a340d/core/float/round_spec.rb#L88-L98

nobu/rubyspec,ruby/rubyspec,eregon/rubyspec,ruby/spec,nobu/rubyspec,eregon/rubyspec,sgarciac/spec,eregon/rubyspec,sgarciac/spec,ruby/spec,ruby/spec,sgarciac/spec,nobu/rubyspec,ruby/rubyspec