yield a block to RedCheck.check() when it evaluates to true.

yield a block to RedCheck.check() when it evaluates to true, so you can say:

RedCard.check("1.9") do
  puts "I'm on 1.9"
end
use "or" like rest of RedCard.
Merge pull request #4 from robgleeson/check_yields_block

yield a block to RedCheck.check() when it evaluates to true.